Melanocortin Metallopeptode Combinatorial Libraries and Applications

ABSTRACT

Melanocortin receptor-specific peptide combinatorial libraries for forming metallopeptides and metallopeptide combinatorial libraries are provided for use in biological, pharmaceutical and related applications. The combinatorial libraries are constructed of peptides constructed from naturally occurring amino acids, stereoisomers and modifications of such amino acids, non-protein amino acids, post-translationally modified amino acids, enzymatically modified amino acids, or constructs or structures designed to mimic amino acids, in which the peptides are conformationally fixed on complexation of a metal ion-binding portion thereof with a metal ion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent application Ser. No. 10/049,718, entitled Melanocortin Metallopeptide Constructs, Combinatorial Libraries and Applications, filed Feb. 13, 2002, and issued as U.S. Pat. No. 7,049,398 on May 23, 2006, which application is a national entry pursuant to 37 U.S.C. § 371 of International Application No. PCT/US00/16396, entitled Melanocortin Metallopeptide Constructs, Combinatorial Libraries and Applications, filed Jun. 15, 2000, which in turn claims the benefit of the filing of U.S. Provisional Patent Application Ser. No. 60/148,994, entitled Melanocortin Receptor-Specific Metallopeptide Constructs, Combinatorial Libraries and Applications, filed on Aug. 13, 1999, and the specifications thereof are incorporated herein by reference.

GOVERNMENT RIGHTS

The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Grant No. R43 CA83417 awarded by the National Cancer Institute of the National Institutes of Health of the Department of Health and Human Services and Grant No. R43 DK55470 awarded by the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health of the Department of Health and Human Services.

BACKGROUND OF THE INVENTION

1. Field of the Invention (Technical Field)

The present invention relates to metallopeptides, metal ion-complexed peptidomimetics, and metallo-constructs, including metallopeptide combinatorial libraries, metal ion-complexed peptidomimetic and peptide-like combinatorial libraries and metallo-construct combinatorial libraries, specific for melanocortin receptors, including methods for the use and making of the same. The invention also relates to methods for synthesizing and assembling such libraries, and methods for identification and characterization of library constituents which are capable of binding a melanocortin receptor of interest, or mediating a melanocortin receptor-related biological activity of interest.

2. Background Art

Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.

Melanocortin Receptors. A family of melanocortin receptor types and subtypes has been identified, including melanocortin-1 receptors (MC1-R) expressed on normal human melanocytes and melanoma cells, melanocortin-2 receptors (MC2-R) for ACTH (adrenocorticotropin) expressed in cells of the adrenal gland, melanocortin-3 and melanocortin-4 receptors (MC3-R and MC4-R) expressed primarily in cells in the hypothalamus, mid-brain and brainstem, and melanocortin-5 receptors (MC5-R), expressed in a wide distribution of peripheral tissues.

Peptides specific for melanocortin receptors have been reported to have a wide variety of biological activities, including effects upon pigmentation and steroidogenesis, known to be mediated by MSH (melanocyte stimulating hormone) and ACTH receptors. Several studies have documented the presence of melanotropin receptors on primary human melanoma cells (Tatro J B, Atkins M, Mier J W, et al. Melanotropin receptors demonstrated in situ in human melanoma. J Clin Invest, 85:1825-1832, 1990). Melanotropin receptors have been reported as markers for melanotic and amelanotic human melanoma tumors (Sharma S D, Granberry M E, Jiang J, et al. Multivalent melanotropic peptide and fluorescent macromolecular conjugates: new reagents for characterization of melanotropin receptors. J Clin Invest, 85:1825-1832, 1990). Melanotropin receptors have been reported as markers for melanotic and amelanotic human Sharma S D, Jiang J, Hadley M E, et al. Melanotropic peptide-conjugated beads for microscopic visualization and characterization of melanoma melanotropin receptors. Proc Natl Acad Sci USA 93(24):13715-13720, 1996). In particular, the presence of MC1-R has been demonstrated in human melanoma cells by an antibody to MC1-R (Xia Y, Skoog V, Muceniece R, et al. Polyclonal antibodies against human melanocortin MC-1 receptor: Preliminary immunohistochemical localization of melanocortin MC1 receptor to malignant melanoma cells. European J Pharmacol 288:277-283, 1995). MC1-R is a G protein-coupled, 7-transmembrane receptor expressed in skin-cell melanocytes and shares some degree of homology with related receptors MC2-R, MC3-R, MC4-R and MC5-R. Each of these receptors can bind various peptide analogs that contain a common melanotropic pharmacophore, His-Phe-Arg-Trp (SEQ ID NO:1), which describes the 6-9 sequence of the alpha-melanocyte stimulating hormone (α-MSH).

Prior to molecular characterization of the MC receptors, α-MSH analogs were labeled with the radioisotope Indium-111 and used in melanoma imaging studies (Wraight E P, Bard D R, Maughan T S, et al. The use of a chelating derivative of alpha melanocyte stimulating hormone for the clinical imaging of malignant melanoma. Brit J Radiology 65: 112-118, 1992; Bard D R, Knight C G and Page-Thomas D P. A chelating derivative of alpha-melanocyte stimulating hormone as a potential imaging agent for malignant melanoma. Brit J Cancer 62:919-922, 1990; Bard D R, Knight C G, Page-Thomas D P. Targeting of a chelating derivative of a short chain analogue of alpha-melanocyte stimulating hormone to Cloudman S91 melanomas. Biochem Soc Trans 18:882-883, 1990). Linear and cyclic disulfide-containing peptides have been identified and used for melanoma imaging and appear to be non-selective among MC receptors (Chen J and Quinn T P. Alpha melanocyte stimulating hormone analogues Tc-99m/Re-188 labeling and their pharmacokinetics in malignant melanoma bearing mice. J Nucl Med 39: 222p, 1998; Giblin M F, Wang N, Hoffman T J, et al. Design and characterization of alpha-melanotropin peptide analogs cyclized through rhenium and technetium metal coordination. Proc Natl Acad Sci U S A 95(22):12814-12818, 1998). In later studies, the cyclic peptide reported by Giblin and coworkers was also found to localize in the brain (Wang N N, Giblin M F, Hoffman T J, et al. In vivo characterization of Tc-99m and Re-188 labeled cyclic melanotropin peptide analogues in a murine melanoma model. J Nucl Med 39: 77p, 1998 and corresponding poster presentation at the 45th Society of Nuclear Medicine Meeting, Toronto, June 1998). It has been recently reported that the response of human melanocytes to UV radiation is mediated by α-MSH induced activation of the cAMP pathway through the MC1-R (Im S, Moro O, Peng F, et al. Activation of the cyclic AMP pathway by alpha-melanotropin mediates the response of human melanocytes to ultraviolet B radiation. Cancer Res 58: 47-54, 1998).

MC4-R is also a G protein-coupled, 7-transmembrane receptor, but is believed to be expressed primarily in the brain. Inactivation of this receptor by gene targeting has been reported to result in mice with the maturity-onset obesity syndrome that is associated with hyperphagia, hyperinsulinemia, and hyperglycemia (Huszar D, Lynch C A, Fairchild-Huntress V, et al. Targeted disruption of the melanocortin-4 receptor results in obesity in mice. Cell 88:131-141, 1997). MC4-R is a molecular target for therapeutic intervention in energy homeostasis.

Alpha-MSH has been described as a potent anti-inflammatory agent in all major forms of inflammation (Star R A, Rajora N, Huang J, Stock R C, Catania A, and Lipton J M: Evidence of autocrine modulation of macrophage nitric oxide synthase by alpha-melanocyte stimulating hormone. Proc Natl Acad Sci U S A 92:8016-8020, 1995; Getting S J, and Perretti M: MC3-R as a novel target for antiinflammatory therapy. Drug News and Perspectives 13:19-27, 2000). Implication of both MC1-R and MC3-R receptors in anti-inflammatory processes has been stressed. In particular, the activation of these MC receptors by melanocortin receptor agonists has been reported to inhibit the expression of nitric oxide synthase and subsequent nitric oxide production.

Significant work has been done in determining the structure of melanocortin receptors, including both the nucleic acid sequences encoding for the receptors and the amino acid sequences constituting the receptors. See, for example, International Patent Applications No. PCT/US98/12098 and PCT/US99/16862 and U.S. Pat. No. 5,994,087. A large number of ligands specific for melanocortin receptors, both agonists and antagonists, have also been developed. See, for example, International Patent Applications No. PCT/US98/03298 (iodo group-containing melanocortin receptor-specific linear peptide), PCT/GB99/01388 (MC1-R specific linear peptides), PCT/GB99/01195 (MC3-R, MC4-R and MC5-R specific cyclic peptides), PCT/US99/04111 (MC1-R specific peptide antagonists for melanoma therapy), PCT/US99/09216 (isoquinoline compounds as melanocortin receptor ligands), PCT/US99/13252 (spiropiperdine derivatives as melanocortin receptor agonists), and U.S. Pat. No. 6,054,556 (cyclic lactam peptides as MC1-R, MC3-R, MC4-R and MC5-R antagonists). In addition, a large number of patents teach various methods of screening and determining melanocortin receptor-specific compounds, as for example International Patent Applications No. PCT/US97/15565, PCT/US98/12098 and PCT/US99/16862 and U.S. Pat. Nos. 5,932,779 and 5,994,087.

In general, compounds specific for MC1-R are believed to be useful for treatment of melanoma, including use as radiotherapeutic or drug delivery agent, and as diagnostic imaging agents, particularly when labeled with a diagnostic radionuclide. Compounds specific for MC3-R, MC4-R or MC5-R are believed to be useful in regulation of energy homeostasis, including use as agents for attenuating food intake and body weight gain, for use in treatment of anorexia, as a weight gain aid, for treatment of obesity, and other treatment of other food intake and metabolism-related purposes. Compounds specific for MC3-R and MC4-R, among other melanocortin receptors, can be used as agents for treatment of sexual dysfunction, including male erectile dysfunction. Compounds specific for MC3-R and MC4-R, among other melanocortin receptors, can be used to regulate blood pressure, heart rate and other neurophysiologic parameters. Other melanocortin receptor peptides can be used as tanning agents, to increase melanin production, such as peptides that are MCR-1 agonists. Compounds specific for MCR-1 and MCR-3 may be useful in regulation of inflammatory processes.

There remains a significant need for ligands with high specificity for discrete melanocortin receptors, as well as ligands or compounds that are either agonists or antagonists of specific melanocortin receptors. High affinity peptide ligands of melanocortin receptors can be used to exploit varied physiological responses associated with the melanocortin receptors, either as agonists or antagonists. In addition, melanocortin receptors have an effect on the activity of various cytokines, and high affinity peptide ligands of melanocortin receptors can be used to regulate cytokine activity.

Peptide Libraries and Combinatorial Chemistry. Libraries of peptides and other small molecules, with enormous pools of structurally diverse molecules, are well suited for pharmaceutical lead generation and lead optimization. Libraries of a variety of molecular species have been described in literature and screened for drug discovery, including peptides, peptoids, peptidomimetics, oligonucleotides, benzodiazepines, and other libraries of small organic molecules. Various approaches have been used to construct libraries of structurally diverse chemical compounds, including chemical synthesis and genetic engineering methods. Chemically synthesized libraries have been synthesized by general solution chemical means and by solid-phase methods. The prior art on designing, synthesizing, screening, and evaluation of peptide-based libraries has been reviewed in numerous articles.

Spatially Addressable Parallel Synthesis of Solid Phase Bound Libraries. Various strategies for chemical construction of a library of peptides or other small molecules are well established. One strategy involves spatially separate synthesis of compounds in parallel on solid phase or on a solid surface in a predetermined fashion so that the location of one compound or a subset of compounds on the solid surface is known. Other methods, such as light-directed spatially addressable parallel chemical synthesis techniques, based upon use of photolithographic techniques in peptide synthesis on a solid surface, such as a borosilicate glass microscope slide, provide libraries containing more than 100,000 spatially separated compounds. However, synthesis of libraries that are structurally more diverse than simple peptides requires the development of orthogonal photolabile protecting groups that can be cleaved at different wavelengths of light. In addition, the solid surface bearing these libraries also has been reported to cause a pronounced effect on binding affinities in library screening assays.

Pooling and Split Synthesis Strategies. Large libraries of compounds can be assembled by a pooling strategy that employs equimolar mixtures of reactants in each synthetic step or by adjusting the relative concentration of various reactants in the mixture according to their reactivities in each of the coupling reactions. In one approach equimolar mixtures of compounds are obtained by splitting the resin in equal portions, each of which is separately reacted with each of the various monomeric reagents. The resin is mixed, processed for the next coupling, and again split into equal portions for separate reaction with individual reagents. The process is repeated as required to obtain a library of desired oligomeric length and size. This approach is the basis of the “one-bead one-peptide” strategy which employs amino acid sequencing to ascertain the primary structure of the peptide on a hit bead in a bioassay. Automated systems have been developed for carrying out split synthesis of these libraries with rather more efficiency. A common artifact occasionally seen with all these resin bound libraries is altered target-specific affinity by some solid phase bound compounds in bioassays, which can result in totally misleading results.

Another strategy involves construction of soluble libraries. This strategy involves a deconvolution process of iterative re-synthesis and bioassaying until all the initially randomized amino acid positions are defined. Several modifications to this strategy have been developed, including co-synthesis of two libraries containing orthogonal pools, which eliminates the need of iterative re-synthesis and evaluation. A major limitation of the soluble library approach is its applicability to high affinity systems. The abundance of each compound in solution can be influenced by the total number of compounds in a library that can affect the biological activity. For this reason, a highly active compound in any pool may not in fact be the most potent molecule. Lack of reasonable solubilities of certain members in a library may further influence this phenomenon.

Among the various classes of libraries of small molecules, peptide libraries remain the most versatile because of the structural diversity offered by the use of naturally occurring amino acids, incorporation of a variety of “designer” amino acids, and the high efficiency and ease with which peptide synthesis can be accomplished. In addition, another level of structural diversity in peptide-based libraries has been added by post-synthesis modification of the libraries. These modifications include permethylation, acylation, functionalization of the side chain functionality, and reductive amination of the N-terminus.

SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)

In one preferred embodiment, the invention provides a combinatorial library targeted to melanocortin receptors of different sequence peptide members synthesized on solid phase, where each constituent library member comprises:

(a) a peptide sequence of three or more amino acid residues bound to solid phase characterized by (i) a sequence of two or more amino acid residues forming a metal ion-binding domain and including at least one amino acid residue containing at least one S wherein the said S is protected by an orthogonal S-protecting group, (ii) a sequence of one or more amino acid residues at the N- or C-terminus of the metal ion-binding domain, or at both the N- and C-terminus of the metal ion-binding domain, and (iii) a cleavable bond attaching the peptide sequence to solid phase; and

(b) a unique selection or sequence of amino acid residues in the peptide sequence of at least one of the constituent members of the library;

-   -   wherein the orthogonal S-protecting group may be removed without         cleaving the peptide sequence from the solid phase.

In another preferred embodiment, the invention provides a combinatorial library targeted to melanocortin receptors of different sequence peptidomimetic members synthesized on solid phase, where each constituent library member comprises:

(a) a peptidomimetic sequence of a combination of three or more amino acid residues and mimics of amino acid residues bound to solid phase characterized by (i) a sequence of two or more amino acid residues, mimics of amino acid residues or combinations thereof forming a metal ion-binding domain and including at least one amino acid residue or mimic of an amino acid residue containing at least one S wherein the said S is protected by an orthogonal S-protecting group, (ii) a sequence of one or more amino acid residues, mimics of amino acid residues or combinations thereof at the N- or C-terminus of the metal ion-binding domain, or at both the N- and C-terminus of the metal ion-binding domain, and (iii) a cleavable bond attaching the peptidomimetic sequence to solid phase; and

(b) a unique selection or sequence of amino acid residues, mimics of amino acid residues or combinations thereof in the peptidomimetic sequence of at least one of the constituent members of the library;

-   -   wherein the orthogonal S-protecting group may be removed without         cleaving the peptidomimetic sequence from the solid phase.

In another preferred embodiment, the invention provides a combinatorial library targeted to melanocortin receptors of different sequence peptide or peptidomimetic members synthesized in solution, where each constituent library member comprises:

(a) a peptidomimetic sequence of a combination of three or more amino acid residues and mimics of amino acid residues characterized by (i) a sequence of two or more amino acid residues, mimics of amino acid residues or combinations thereof forming a metal ion-binding domain and including at least one amino acid residue or mimic of an amino acid residue containing at least one S wherein the said S is protected by an orthogonal S-protecting group, (ii) a sequence of one or more amino acid residues, mimics of amino acid residues or combinations thereof at the N- or C-terminus of the metal ion-binding domain, or at both the N- and C-terminus of the metal ion-binding domain; and

(b) a unique selection or sequence of amino acid residues, mimics of amino acid residues or combinations thereof in the peptidomimetic sequence of at least one of the constituent members of the library.

The libraries of this invention include compositions of the formulas: R₁-Lll-Aaa-Bbb-Ccc-R₂, R₁-Bbb-Aaa-Ccc-R₂, R₁-Ddd-Bbb-Aaa-R₃, R₄-Eee-Bbb-Ccc-R₂, R₁-Fff-Aaa-Ggg-Ccc-R₅, R₁-Hhh-Aaa-Bbb-Ccc-R₅, and R₁-Iii-Iii-Ccc-Jjj-Kkk-R₂,

wherein

-   R₁ is any functionality that potentiates the intrinsic activity of     the remainder of the molecule, including but not limited to     providing an auxiliary or secondary receptor contact. Any of a     variety of amino acids and non-peptide groups may be employed,     including an amino acid chain from one to about four neutral or     charged L- or D-configuration amino acid residues. If R₁ is a     non-peptide group, it may be a linear or branched alkyl, aryl,     alkene, alkenyl or aralkyl chain; -   Aaa is an L- or D-configuration cationic amino acid with a     positively charged side chain. Preferred amino acids include     L-configuration Lys, Arg, Orn, Dpr or Dbu, and derivatives, analogs     or homologs thereof, including both natural and synthetic amino     acids. Aaa provides an N (nitrogen atom) for metal ion complexation; -   Bbb is an L- or D-configuration amino acid with an aromatic side     chain. Preferred amino acids include D-configuration Phe, Phe(4′Cl),     Phe(3′,4′ Di-Cl), Phe(4′-nitro), Phe(4′-methyl), Phe(4′-Phenyl),     Hphe, Pgl, Trp, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br),     Lys(Bz), Thr(Bzl), Cys(Bzl), or Tyr(BzlCl₂), and derivatives,     analogs or homologs thereof. The aromatic ring in Bbb may be     functionalized with halogen, alkyl or aryl groups. Bbb provides an N     for metal ion complexation; -   Ccc is an amino acid that provides both an N, from the alpha amino     group, and an S (sulfur atom), from a side chain group, for metal     ion complexation. Preferred amino acids include L- or     D-configuration Cys, Pen and Hcys; -   Lll is a D-configuration amino acid with an aromatic side chain.     Preferred amino acids include D-configuration Phe, Phe(4′Cl),     Phe(3′,4′ Di-Cl), Phe(4′-nitro), Phe(4′-methyl), Phe(4′-Phenyl),     Hphe, Pgl, Trp, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br),     Lys(Bz), Thr(Bzl), Cys(Bzl), or Tyr(BzlCl₂), and derivatives,     analogs or homologs thereof. The aromatic ring in Lll may be     functionalized with halogen, alkyl or aryl groups. Lll does not     provide an N for metal ion complexation; -   R₂ is an amino acid with an aromatic side chain. Preferred amino     acids include L- or D-configuration Phe, Trp, Phe(4′Cl), Phe(3′,4′     Di-Cl), Phe(4′-nitro), Phe(4′-methyl), Phe(4′-Phenyl), Hphe, Pgl,     Trp, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl),     Cys(Bzl) or Tyr(BzlCl₂), and derivatives, analogs or homologs     thereof, including both natural and synthetic amino acids. The     C-terminus may be free or amidated. R₂ may also be the corresponding     des-carboxyl amino acid of any of the foregoing. Alternatively, R₂     may be eliminated; -   Ddd is an amino acid that provides an S, from a side chain group,     for metal ion complexation. Preferred amino acids include L- or     D-configuration Cys, Pen and Hcys; -   R₃ is an amino acid with an aromatic side chain that provides an N     for metal ion complexation. Preferred amino acids include L- or     D-configuration Phe, Trp, Phe(4′Cl), Phe(3′,4′ Di-Cl),     Phe(4′-nitro), Phe(4′-methyl), Phe(4′-Phenyl), Hphe, Pgl, Trp,     1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl),     Cys(Bzl) or Tyr(BzlCl₂), and derivatives, analogs or homologs     thereof, including both natural and synthetic amino acids. The     C-terminus may be free or amidated. R₃ may also be the corresponding     des-carboxylamino acid of any of the foregoing; -   R₄ is a functionality that provides a cationic center. Preferred     amino acids include L- or D-configuration Lys, Arg, Orn, Dpr or Dbu,     and derivatives, analogs or homologs thereof, including both natural     and synthetic amino acids. The N-terminus of the amino acid may be     functionalized with any of a variety of neutral amino acid and     non-peptide groups, including linear or branched alkyl, aryl,     alkene, alkenyl or aralkyl chains; -   Eee is an uncharged L- or D-configuration amino acid that provides     an N for metal ion complexation. Preferred amino acids include Gly     and L-configuration Ala, Nle, Leu, Val, Phe or Trp, and derivatives,     analogs or homologs thereof, including both natural and synthetic     amino acids. In a preferred embodiment, Eee isn an amino acid with     an aliphatic side chain; -   Fff is an L- or D-configuration aromatic amino acid. Preferred amino     acids include D-configuration Phe, Phe(4′Cl), Phe(3′,4′ Di-Cl),     Phe(4′-nitro), Phe(4′-methyl), Phe(4′-Phenyl), Hphe, Pgl, Trp,     1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl),     Cys(Bzl), Tyr(BzlCl₂), Tic, Tiq or Tca, and derivatives, analogs or     homologs thereof, including both natural and synthetic amino acids.     The aromatic ring in Fff may be substituted with halogen, alkyl or     aryl groups. Fff does not provide an N for metal ion complexation; -   Ggg is an L- or D-configuration aromatic amino acid. Preferred amino     acids include L-configuration Phe, Phe(4′Cl), Phe(3′,4′ Di-Cl),     Phe(4′-nitro), Phe(4′-methyl), Phe(4′-Phenyl), Hphe, Pgl, Trp,     1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl),     Cys(Bzl) or Tyr(BzlCl₂), and derivatives, analogs or homologs     thereof, including both natural and synthetic amino acids. The     aromatic ring in Ggg may be substituted with halogen, alkyl or aryl     groups. Ggg provides an N for metal ion complexation; -   R₅ is preferably an amide, substituted amide, ester or carboxylate     group. R₅ may also be and L- or D-configuration amino acid or amino     acid amide, including an aromatic, aliphatic, neutral or charged     amino acid; -   Hhh is an L- or D-configuration cationic amino acid with a     positively charged side chain. Preferred amino acids include     L-configuration Lys, Arg, Orn, Dpr or Dbu, and derivatives, analogs     or homologs thereof, including both natural and synthetic amino     acids. Hhh does not provide an N for metal ion complexation; -   Iii is an L- or D-configuration amino acid that provides an N for     metal ion complexation. Preferred amino acids includes Ala, Gly,     Nle, Val. Leu, Ile, His, Lys, or Arg, and derivatives, analogs or     homologs thereof, including both natural and synthetic amino acids; -   Jjj is an L- or D-configuration amino acid with an aromatic side     chain. Preferred amino acids include D-configuration Phe, Phe(4′Cl),     Phe(3′,4′ Di-Cl), Phe(4′-nitro), Phe(4′-methyl), Phe(4′-Phenyl),     Hphe, Pgl, Trp, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br),     Lys(Bz), Thr(Bzl), Cys(Bzl), or Tyr(BzlCl₂), and derivatives,     analogs or homologs thereof. The aromatic ring in Jjj may be     functionalized with halogens, alkyl or aryl groups. Jjj does not     provide an N for metal ion complexation; and -   Kkk is an L- or D-configuration cationic amino acid with a     positively charged side chain. Preferred amino acids include     L-configuration Lys, Arg, Orn, Dpr or Dbu, and derivatives, analogs     or homologs thereof, including both natural and synthetic amino     acids. Aaa does not provide an N for metal ion complexation.

In the compositions of this invention, the metal ion-binding domain can be complexed with a metal ion, and such compositions are included within the invention. The invention further includes compositions wherein the composition is substantially more specific for one or more melanocortin receptors when the metal ion-binding domain is complexed with a metal ion than is the composition when the metal ion-binding amino acid sequence is not complexed with a metal ion.

The combinatorial libraries of this invention include libraries wherein the metal ion-binding domain further comprises at least one N available for binding to a metal ion upon removal of the orthogonal S-protecting group. The combinatorial libraries include compositions wherein the metal ion-binding domain comprises three residues forming an N₃S₁ ligand.

In the combinatorial libraries, the orthogonal S-protecting group is S-thio-butyl, acetamidomethyl, 4-methoxytrityl, S-sulfonate or 3-nitro-2-pyridinesulfenyl. The orthogonal S-protecting group may be removed from constituent library members thereof without otherwise altering the constituent library members or any amino acid side chain protecting group therein. In the combinatorial libraries, structural diversity may occurs in the metal ion-binding domain or outside the metal ion-binding domain.

In the combinatorial libraries, one or more constituent library members may include at least one amino acid residue or mimic of an amino acid residue in the sequence at the N- or C-terminus of the metal ion-binding domain containing at least one S wherein the said S is protected by a non-orthogonal S-protecting group, whereby the orthogonal S-protecting group may be removed without removing the non-orthogonal S-protecting group.

For combinatorial libraries limited to amino acids, the amino acid residue containing at least one S wherein the said S is protected by an orthogonal S-protecting group can be an L- or D-3-mercapto amino acid, including but not limited to L- or D-cysteine or L- or D-penicillamine. For combinatorial libraries including amino acid residues and mimics of amino acid residues, the residue containing at least one S wherein the said S is protected by an orthogonal S-protecting group can be an L- or D-3-mercapto amino acid, including but not limited to L- or D-cysteine or L- or D-penicillamine; 3-mercapto phenylananine; 2-mercaptoacetic acid; 3-mercaptopropionic acid; 2-mercaptopropionic acid; 3-mercapto-3,3,-dimethyl propionic acid; 3-mercapto-3,3,-diethyl proprionic acid; 3-mercapto, 3-methyl propionic acid; 2-mercapto,2-methyl acetic acid; 3-cyclopentamethylene,3-mercaptopropionic acid; or 2-cyclopentamethylene,2-mercaptoacetic acid.

It is an object of this invention to devise, demonstrate and illustrate the preparation and use of highly specific conformationally restricted peptides, peptoids, related pseudopeptides, peptidomimetics and metallo-constructs formed by complexing sequences thereof to a desired metal ion so that the topography of the side chains in the resulting complex is a biologically active three-dimensional structure specific for melanocortin receptors.

Another object of this invention is to provide peptide-metal ion complexes specific for melanocortin receptors and which have a higher level of stability and are less susceptible to proteolysis than either the uncomplexed peptide, or other peptides known in the art.

Another object of this invention is to provide peptide-metal ion complexes that are specific for different subsets of melanocortin receptors, such as specific only for MC1-R or for MC4-R.

Another object of this invention is to provide peptide-metal ion complexes which are specific for melanocortin receptors and which are agonists or antagonists.

Another object of this invention is to provide for peptide analogs which are not conformationally restricted in the absence of a metal ion, whereby the uncomplexed peptide analog is either inactive or demonstrates low potency, but which is conformationally restricted on complexation with a metal ion and specific for melanocortin receptors with high potency.

Another object of this invention is to utilize metal complexation in a peptide specific for melanocortin receptors to cause specific regional conformational restrictions in the peptide so that the peptide conformation at the metal binding site is conformationally fixed on metal complexation.

Another object of this invention is to complex a peptide to a metal ion, whereby the resulting metallopeptide is specific for melanocortin receptors, and exhibits a preferred in vivo biodistribution profile, rate and mode of clearance, bioavailability and pharmacokinetics in mammals.

Another object of this invention is to provide peptide-metal ion complexes specific for melanocortin receptors utilizing stable non-radioactive metal ions, for use in therapeutic treatment of disease, including as an agent to modify energy metabolism and feeding behavior, such as for treatment of pathologic obesity and related conditions.

Another object of this invention is to provide peptide-metal ion complexes specific for melanocortin receptors utilizing metal ions which are radionuclides for use in diagnostic methods, including imaging and staging of melanoma tumors and melanoma tumor metastases.

Another object of this invention is to provide peptide-metal ion complexes specific for melanocortin receptors utilizing stable non-radioactive metal ions, for use as a prevention agent against ultra-violet radiation-induced DNA damages, including sunlight-induced DNA damage in the skin.

Another object of this invention is to provide peptide-metal ion complexes specific for melanocortin receptors utilizing stable non-radioactive metal ions, for use as a tanning agent, including but not limited to therapeutic use as a tanning agent.

Another object of this invention is to provide peptide-metal ion complexes specific for melanocortin receptors utilizing stable non-radioactive metal ions, for use as anti-inflammatory agents.

Another object of this invention is to complex peptides with radiometal ions, including but not limted to technetium-99m, for use in diagnostic imaging, so that the resulting peptide-metal ion complex is substantially more specific for melanocortin receptors than the uncomplexed peptide molecule, and the resulting radiolabeled species is essentially carrier-free in terms of specificity for melanocortin receptors.

Another object of this invention is to complex peptides with radiometal ions, including radioisotopes of rhenium such as rhenium-186 and rhenium-188, for use in targeted radiotherapy, such as for treatment of melanoma.

Another object of this invention is to provide peptide-metal ion complexes specific for melanocortin receptors that can transit the gut-blood barrier, without significant enzymatic or peptidase degradation, and may be adapted for oral administration.

Another object of this invention is to provide libraries of conformationally constrained peptide-metal ion complexes directed to melanocortin receptors.

Another object of this invention is to provide combinatorial peptide libraries of peptide-metal ion complexes specific for melanocortin receptors, wherein the peptides include a metal ion-binding domain, such that a specific conformational restriction is obtained upon labeling the peptides with a metal ion.

Another object of this invention is to provide combinatorial peptide libraries of peptide-metal ion complexes specific for melanocortin receptors, wherein the amino acids comprising the peptides may be naturally occurring amino acids, isomers and modifications of such amino acids, non-protein amino acids, post-translationally modified amino acids, enzymatically modified amino acids, constructs or structures designed to mimic amino acids, and the like, so that the library includes pseudopeptides and peptidomimetics.

Another object of this invention is to provide metallopeptide libraries specific for one or more melanocortin receptors, wherein the metallopeptides include a metal ion-binding domain, such that a determined conformational restriction is obtained upon labeling the peptides with a metal ion, and the metallopeptides further include distinct, unique and different amino acid sequences.

Another object of this invention is to provide both soluble and solid phase metallopeptide libraries specific for one or more melanocortin receptors, wherein the metallopeptides include a metal ion-binding domain.

Another object of this invention is to provide methods for synthesis of peptides specific for melanocortin receptors wherein the peptide contains a reactive SH group forming a part of a metal ion-binding domain, whereby the reactive SH group is protected during synthesis, and is deprotected only upon complexing the peptides with a metal ion.

Another object of this invention is to provide combinatorial metallopeptide libraries specific for melanocortin receptors wherein the peptides forming the library contain a reverse turn structure as a consequence of metal ion complexation.

Another object of this invention is to provide a method for rapid and efficient complexation of a pool of diverse peptides specific for melanocortin receptors with a metal ion, including a rhenium metal ion.

Another object of this invention to provide libraries of conformationally constrained peptide-metal ion complexes as surrogates for reverse turn structures, such as beta turns and gamma turns commonly found in naturally occurring peptides and proteins specific for melanocortin receptors. The turns formed as a consequence of metal ion complexation are more stable than the naturally occurring turn structures, which are stabilized only by weaker interactions such as van der Waals=interactions and hydrogen bonds.

Another object of this invention is to provide combinatorial metallopeptide libraries wherein each of the peptides forming the library contain a reverse turn structure as a consequence of metal ion complexation.

Another object of this invention is to provide a method for the identification of specific metallopeptides through internal signatures resulting from use of metal ions with two or more isotopic peaks, such as through use of rhenium containing two isotopes in fixed relative abundance that differ in mass by 2 units.

Other objects, advantages and novel features, and the further scope of applicability of the present invention, will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of this invention. The objects and advantages of this invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a part of the specification, illustrate several embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating a preferred embodiment of the invention and are not to be construed as limiting the invention. In the drawings:

FIG. 1 is a molecular structure for Template 1.

FIG. 2 is a molecular structure for Template 2.

FIG. 3 is a molecular structure for Template 3.

FIG. 4 is a molecular structure for Template 4.

FIG. 5 is a molecular structure for Template 5.

FIG. 6 is a molecular structure for Template 6.

FIG. 7 is a molecular structure for Template 7.

FIG. 8 is a flow chart of a split pool and combination synthesis method according to Example 2.

FIG. 9 is a mass spectrum of a library pool of 25 metallopeptides synthesized according to Example 2.

FIG. 10 is a mass spectrum of a library pool of 4 metallopeptides synthesized according to Example 6.

FIGS. 11A-11E are reversed phased HPLC profiles of a library pool of 4 metallopeptides synthesized according to Example 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (BEST MODES FOR CARRYING OUT THE INVENTION)

Definitions. Certain terms as used throughout the specification and claims are defined as follows:

The terms “bind,” “binding,” “complex,” and “complexing,” as used throughout the specification and claims, are generally intended to cover all types of physical and chemical binding, reactions, complexing, attraction, chelating and the like.

The “peptides” of this invention can be a) naturally-occurring, b) produced by chemical synthesis, c) produced by recombinant DNA technology, d) produced by biochemical or enzymatic fragmentation of larger molecules, e) produced by methods resulting from a combination of methods a through d listed above, or f) produced by any other means for producing peptides.

By employing chemical synthesis, a preferred means of production, it is possible to introduce various amino acids which do not naturally occur along the chain, modify the N- or C-terminus, and the like, thereby providing for improved stability and formulation, resistance to protease degradation, and the like.

The term “peptide” as used throughout the specification and claims is intended to include any structure comprised of two or more amino acids, including chemical modifications and derivatives of amino acids. For the most part, the peptides of this invention comprise fewer than 100 amino acids, and preferably fewer than 60 amino acids, and most preferably ranging from about 2 to 20 amino acids. The amino acids forming all or a part of a peptide may be naturally occurring amino acids, stereoisomers and modifications of such amino acids, non-protein amino acids, post-translationally modified amino acids, enzymatically modified amino acids, constructs or structures designed to mimic amino acids, and the like, so that the term “peptide” includes pseudopeptides and peptidomimetics, including structures which have a non-peptidic backbone. The term “peptide” also includes dimers or multimers of peptides. A “manufactured” peptide includes a peptide produced by chemical synthesis, recombinant DNA technology, biochemical or enzymatic fragmentation of larger molecules, combinations of the foregoing or, in general, made by any other method.

The “amino acids” used in this invention, and the term as used in the specification and claims, include the known naturally occurring protein amino acids, which are referred to by both their common three letter abbreviation and single letter abbreviation. See generally Synthetic Peptides: A User's Guide, GA Grant, editor, W.H. Freeman & Co., New York, 1992, the teachings of which are incorporated herein by reference, including the text and table set forth at pages 11 through 24. As set forth above, the term “amino acid” also includes stereoisomers and modifications of naturally occurring protein amino acids, non-protein amino acids, post-translationally modified amino acids, enzymatically synthesized amino acids, derivatized amino acids, constructs or structures designed to mimic amino acids, and the like. Modified and unusual amino acids are described generally in Synthetic Peptides: A User's Guide, cited above; Hruby V J, Al-obeidi F and Kazmierski W: Biochem J 268:249-262, 1990; and Toniolo C: Int J Peptide Protein Res 35:287-300, 1990; the teachings of all of which are incorporated herein by reference. In addition, the following abbreviations have the meanings giving: Abu gamma-amino butyric acid 2-Abz 2-amino benzoic acid 3-Abz 3-amino benzoic acid 4-Abz 4-amino benzoic acid Achc 1-amino-cyclohexane-1-carboxylic acid Acpc 1-amino-cyclopropane-1-carboxylic acid 12-Ado 12-amino dodecanoic acid 7-Ahept 7-amino heptanoic acid Aic 2-aminoindane-2-carboxylic acid 6-Ahx 6-amino hexanoic acid 8-Aoc 8-amino octanoic acid Arg(Tos) N^(G)-para-tosyl-arginine Asp(anilino) beta-anilino-aspartic acid Asp(3-Cl-anilino) beta-(3-chloro-anilino)-aspartic acid Asp(3,5-diCl-anilino) beta-(3,5-dichloro anilino)-aspartic acid D/L Atc (D,L)-2-aminotetralin-2-carboxylic acid 11-Aun 11-amino undecanoic acid AVA 5-amino valeric acid Bip biphenylalanine Bz Benzoyl Cha Cyclohexylalanine Chg Cyclohexylglycine Dip 3,3-Diphenylalanine Et- Ethyl GAA epsilon-guanidino acetic acid GBzA 4-guanidino benzoic acid B-Gpa 3-guanidino propionic acid GVA(Cl) beta-chloro-epsilon-guanidino valeric acid Hphe Homophenylalanine Inp isonipecotic acid Lys(Z) N-epsilon-benzyloxycarbonyl-lysine Me- Methyl Nal 1 3-(1-naphthyl)alanine Nal 2 3-(2-naphthyl)alanine (N-Bzl)Nal 2 N-benzyl-3-(2-naphthyl) alanine (N-PhEt)Nal 2 N(2-phenylethyl)-3-(2-naphthyl) alanine Phg Phenylglycine pF-Phe para-fluoro-phenylalanine Phe(4-Br) 4-bromo-phenylalanine Phe(4-CF₃) 4-trifluoromethyl-phenylalanine Phe(4-Cl) 4-chloro-phenylalanine Phe(2-Cl) 2 chloro-phenylalanine Phe(2,4-diCl) 2,4,-dichloro-phenylalanine Phe(3,4-diCl) 3,4,-dichloro-phenylalanine Phe(3,4-diF) 3,4,-difluoro-phenylalanine Phe(4-I) 4-iodo-phenylalanine Phe(3,4-di-OMe) 3,4,-dimethoxy-phenylalanine Phe(4-Me) 4-methyl-phenylalanine Phe(4-NO₂) 4-nitro-phenylalanine Pip Pipecolic acid Qal(2′) beta-(2-quinolyl)-alanine Sal 3-styrylalanine TFA trifluoroacetyl Tic 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid Tle tert-butylalanine Tyr(Bzl) O-benzyl-tyrosine Tyr(BzlDiCl 2,6) O-(2,6 dichloro)benzyl-tyrosine

A single amino acid, including stereoisomers and modifications of naturally occurring protein amino acids, non-protein amino acids, post-translationally modified amino acids, enzymatically synthesized amino acids, derivatized amino acids, constructs or structures designed to mimic amino acids, and the like, including all of the foregoing, is sometimes referred to herein as a “residue.”

The library constructs of this invention also include a metal ion, which may be an ionic form of any element in metallic form, including but not limited to metals and metalloids. The metal ion may, but need not, be radioactive, paramagnetic or superparamagnetic. The metal ion can be of any oxidation state of any metal, including oxidation states of vanadium (V), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), arsenic (As), selenium (Se), yttrium (Y), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), indium (In), tin (Sn), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), thallium (TI), lead (Pb), bismuth (Bi), polonium (Po), astatine (At), samarium (Sm), europium (Eu), and gadolinium (Gd). The metal ion can also be a radionuclide of any of the foregoing, including In, Au, Ag, Hg, Tc, Re, Sn, At, Y and Cu. A preferred metal ion with a tetradentate coordination sphere is Re. For radiopharmaceutical applications, or applications wherein a radioisotope is desirable for screening, an alpha-, gamma- or beta-emitting radionuclide may be employed.

The coordination sphere of various common metal ions, in general, is tetradentate to hexadentate. In one embodiment according to this invention, an amino acid or amino acid mimetic sequence is included within each library member such that it contains the desired number of groups (4 to 6 in most cases) for complexing with the metal. The molecule is designed so that, upon complexing with a metal, it forms a mimic of a reverse turn structure about the site of metal complexation. A metal with coordination number 4, 5 or 6, and complexing respectively with an amino acid sequence forming a tetra, penta, or hexadentate ligand, will fold and constrain the ligand. The amino acid or amino acid mimetic sequence forming a ligand is defined as the metal ion-binding domain (“MBD”) of the peptide or peptidomimetic. A highly flexible molecule like a peptide, in other words, is folded to form a kind of reverse turn upon its complexation with a metal. This resulting turn is a highly constrained structure in the conformational sense.

The biological-binding domain (“BBD”) of the peptide or peptidomimetic is defined in the specification and claims as a sequence of one or more amino acids which constitute a biologically active sequence, exhibiting binding to a melanocotin-associated receptor, including MC1-R, MC2-R, MC3-R, MC4-R and MC5-R, thereby constituting the peptide as a member of a specific binding pair. The BBD also includes any sequence, which may be consecutive amino acids or mimetics (sychnological) or non-consecutive amino acids or mimetics (rhegnylogical) which forms a melanocortin-associated ligand, which ligand is capable of forming a specific interaction with its acceptor or receptor. The term “receptor” is intended to include both acceptors and receptors. The receptor may be a biological receptor. The sequence or BBD may transmit a signal to the cells, tissues or other materials associated with the biological receptor after binding, but such is not required. The BBD may be either an agonist or antagonist, or a mixed agonist-antagonist. A peptide or peptidomimetic complexed to a metal ion with such a BBD constitutes a member of a “specific binding pair,” which specific binding pair is made up of at least two different molecules, where one molecule has an area on the surface or in a cavity which specifically binds to a particular spatial and polar organization of the other molecule. Frequently, the members of a specific binding pair are referred to as ligand and receptor or anti-ligand.

The BBD is further defined to include the portion of a construct, wherein the construct is a peptidomimetic, peptide-like, or metallo-construct molecule, which upon binding of the construct with a metal ion, is biologically active, exhibiting binding to a melanocortin receptor found on cells, tissues, organs and other biological materials. The BBD may, in this instance, be sychnological or rhegnylogical, and generally has the attributes and functions of a BBD of a peptide. The BBD may be coextensive with all or a portion of the MBD, so that the same amino acids or other residues which constitute the MBD also constitute all or a part of the BBD. In some instances, one or amino acids of the MBD will form a part of the BBD, and one or more additional amino acids, which are not part of the MBD, form the remainder of the BBD.

Conformational constraint refers to the stability and preferred conformation of the three-dimensional shape assumed by a peptide or other construct. Conformational constraints include local constraints, involving restricting the conformational mobility of a single residue in a peptide; regional constraints, involving restricting the conformational mobility of a group of residues, which residues may form some secondary structural unit; and global constraints, involving the entire peptide structure. See generally Synthetic Peptides: A User's Guide, cited above.

The primary structure of a peptide is its amino acid sequence. The secondary structure deals with the conformation of the peptide backbone and the folding up of the segments of the peptide into regular structures such as α-helices, β-sheets, turns and the like. Thus, the three-dimensional shape assumed by a peptide is directly related to its secondary structure. See generally Synthetic Peptides: A User's Guide, cited above, including the text, figures and tables set forth at pages 24-33, 39-41 and 58-67. A global structure refers to a peptide structure which exhibits a preference for adopting a conformationally constrained three-dimensional shape.

The product resulting from the methods set forth herein can be used for both medical applications and animal husbandry or veterinary applications. Typically, the product is used in humans, but may also be used in other mammals. The term “patient” is intended to denote a mammalian individual, and is so used throughout the specification and in the claims. The primary applications of this invention involve human patients, but this invention may be applied to laboratory, farm, zoo, wildlife, pet, sport or other animals. The products of this invention may optionally employ radionuclide ions, which may be used for diagnostic imaging purposes or for radiotherapeutic purposes.

Peptide and Metallo-Construct Molecule Libraries and Combinatorial Chemistries. Using the methods of this invention, libraries of peptides and peptidomimetics are designed wherein each constituent library member includes an MBD sequence necessary for providing a coordination site for complexation with a metal, it being understood that such sequence may differ among the constituent members of the library. Upon complexing the MBD with a metal, a specific structure results, forming a mimic of a reverse turn structure. The specific stereochemical features of this complex are due to the stereochemistry of the coordination sphere of the complexing metal ion. Thus the preferred geometry of the coordination sphere of the metal dictates and defines the nature and extent of conformational restriction.

Libraries of this invention contain constituents which are either locally or globally constrained structures. Libraries may include molecules with either local conformation restrictions or global conformation restrictions, or some combination thereof. This aspect of the invention includes a variety of methods of synthesis, screening and structural elucidation of positive hits in screening systems. The importance of these aspects is well known to those skilled in the art and will also become evident from the following description and examples.

In general, most of the metals that may prove useful in this invention have a coordination number of 4 to 6, and rarely as high as 8, which implies that the putative MBD must be made of residues with reactive groups located in a stereocompatible manner so as to establish a bond with a metal ion of given geometry and coordination sphere. Coordinating groups in the peptide chain include nitrogen atoms of amine, amide, imidazole, or guanidino functionalities; sulfur atoms of thiols or disulfides; and oxygen atoms of hydroxy, phenolic, carbonyl, or carboxyl functionalities. In addition, the peptide chain or individual amino acids can be chemically altered to include a coordinating group, such as oxime, hydrazino, sulfhydryl, phosphate, cyano, pyridino, piperidino, or morpholino groups. For a metal with a coordination number of 4, a tetrapeptide amino acid sequence may be employed (such as Gly-Gly-Gly-Gly (SEQ ID NO:2)), or a tripeptide amino acid sequence in which at least one of the amino acids has a side chain with a coordinating group can similarly be employed (such as Gly-Gly-Cys). The side chain can have a nitrogen, oxygen or sulfur-based coordination group. Thus, an amino acid sequence can provide an N₄, N₃S, N₂S₂, NS₃, N₂SO or similar ligand, yielding tetradentate coordination of a metal ion utilizing nitrogen, sulfur and oxygen atoms.

In another embodiment of the invention, the MBD includes one or more amino acid residues and one or more derivatized amino acids or spacer sequences, with the derivatized amino acid or spacer sequence having a nitrogen, sulfur or oxygen atom available for complexing with the various oxidation states of the metal. Examples of derivatized amino acids include amide, primary alkyl or aryl amide, 1,2,3,4-tetrahydroisoquinoline-2-carboxylic acid and its corresponding 7-hydroxy derivative, N-carboxymethylated amino acids, 2′-mercapto-Trp, N^(β)-(2 mercaptoethane)-α,β-diaminopropionic acid and similar higher homologs of other homologous amino acids, N^(β)-(2 aminoethane)-α,β-diaminopropionic acid and similar higher homologs of other homologous amino acids, N^(β)-(picolinoyl)-α,β-diaminopropionic acid and similar higher homologs of other homologous amino acids, β-(picolylamide)-Asp and similar homologs of other homologous amino acids, N^(β)-(2-amino-benzoyl)-α,β-diaminopropionic acid and similar higher homologs of other homologous amino acids, β-(2-amidomethylpyridine)-Asp and similar homologs of other homologous amino acids, N-benzyloxycarbonyl amino acid, N-tert butyloxycarbonyl amino acid, N-fluorenylmethyloxycarbonyl amino acid and other similar urethane-protected amino acid derivatives, and other derivatized or synthetic amino acids relating to any of the foregoing. Examples of spacer sequences which may be employed in this invention include 2-mercaptoethylamine, succinic acid, glutaric acid, 2-mercaptosuccinic acid, ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentaamine, glycol, polyethylene glycol, thioglycolic acid, mercaptopropionic acid, pyridine-2-carboxylate, picolylamine, 2-mercaptoaniline, 2-aminobenzoic acid, and 2-aminomethylpyridine. In general, any sequence which may be linked, directly or indirectly, to one or two amino acids so as to form a continuous sequence, and which has a nitrogen, sulfur or oxygen atom available for complexing with the valences of the metal ion, may be employed as an element of the MBD.

S-Protected Thiol Group Compounds in Metallo-Libraries. A free thiol (SH) group is preferred for complexation of most metal ions to the peptides and peptidomimetics of this invention, and in many cases an SH group is necessary in order to form a stable exchange-inert complex with a metal. Peptides and other organic molecules with free SH groups, however, are easily oxidized in air and in solution, and can often form a disulfide-linked dimer. If more than one free SH group is present in a molecule, oxidation may lead to a complex polymer. Similarly, if a mixture of different peptides or organic molecules with free SH groups are prepared, oxidation generally leads to a complex mixture of polymers of unknown composition. This is of serious concern in preparing libraries of metallopeptides or other organic molecules where one or more SH group is intended for use in metal complexation.

A variety of SH protecting groups have been employed for a variety of purposes, including radiopharmaceutical manufacture and formulation. For example, in its protected form S-Benzoyl-mercaptoacetyl-glycyl-glycyl-glycine (Bz-MAG₃) has been used to complex Tc-99m (^(99m)Tc) under conditions where the S-Bz group splits during ^(99m)Tc complexation. The use of S-Bz protection, however, is not compatible with the methods of peptide synthesis.

In order to construct metallopeptide libraries of this invention which incorporate an SH group, if mixed pool synthesis is employed the peptides must be S-protected derivatives. The SH protecting group is chosen such that (a) the synthesis of peptide derivatives with S-protecting group is compatible with methods of solution and solid phase peptide synthesis, so that the S-protecting group is stable during synthetic procedures, and (b) the S-protecting group can be deprotected in situ, without cleavage from the resin in the case of solid phase synthesis, during the metal complexation step. Many prior art methods, such as Bz-MAG₃, meet at most only one of the two criteria specified above (Bz-MAG₃ meets only criterion (a) above).

Use of orthogonally S-protected thiol groups permits synthesis of metallo-compounds in a single pot. A mixture of compounds, each compound containing an orthogonal S-protected group (“OSPG”), is used for complexation with a metal ion, and it is only during metal ion complexation that the S-protected group is deprotected, and accordingly polymerization and cross-linking is avoided. This procedure thus provides homogenous libraries of metallo-compounds.

One OSPG meeting the criteria specified above, and which can be used in this invention, employs an S^(t)Bu (S-thio-butyl or S-t-butyl) group to protect the SH group. The S^(t)Bu group is stable under both the acidic and basic conditions typically employed in peptide synthesis. Further, the S^(t)Bu group may be cleaved by reduction using a suitable phosphine reagent, which reduction step may be employed immediately prior to or in conjunction with complexation of a metal ion to the peptide. Such OSPG cleavage does not cleave the peptide from the resin, or otherwise alter the structure of the peptide.

Another OSPG meeting the criteria specified above and suitable for this invention employs an S-Acm (S-acetamidomethyl) group to protect the SH group. The Acm group is also stable under the acid and base conditions usually employed during peptide synthesis. The S-Acm group may be removed by treatment of S-Acm-protected peptide or peptide resin with mercury (II) acetate or silver (I) tertrafluoroborate, which liberates the thiol peptide in its mercury or silver ion-complexed state. Free thiol-containing peptide can then be recovered by treating the mercury or silver ion and thiol complexed salts with an excess of a thiol-containing reagent, such as beta-mercaptoethanol or dithiothreitol. The resulting peptide is then used for metal complexation. Alternatively, the mercury or silver ion and thiol complexed peptide may be directly treated with a metal ion complexing reagent to form the desired metallopeptide.

Other examples of OSPGs for metallopeptides include 4-methoxytrityl (Mmt), 3-nitro-2-pyridinesulfenyl (Npys) and S-sulfonate (SO₃H). Mmt is selectively removed upon treatment with 1% TFA in dichloromethane. Npys and S-sulfonate are selectively removed by treatment with a thiol-containing reagent such as beta-mercaptoethanol or dithiothreitol or a phosphine reagent such as tributyl phosphine. The Npys group (R. G. Simmonds R G et al: Int J Peptide Protein Res, 43:363, 1994) is compatible with Boc chemistry for peptide synthesis and the S-sulfonate (Maugras I et al: Int J Peptide Protein Res, 45:152, 1995) is compatible with both Fmoc and Boc chemistries. Similar OSPGs derived from homologous series of S-alkyl, or S-aryl, or S-aralkyl may also be used in this invention. A primary characterization of the OSPG is that its use results in the formation of a disulfide (S—S) bond utilizing one sulfur atom each from the thiol-containing amino acid and the protecting group. In addition, the resulting disulfide (S—S) bond is cleavable by the use of any of a variety of disulfide cleaving agents, including but not limited to phosphine- and thiol-containing reagents.

The method employing S^(t)Bu protected SH groups, or other OSPGs, may be employed for the generation of either solid phase or soluble libraries. For solid phase libraries, peptides may be synthesized by use of conventional Fmoc chemistry. In the case of conventional Fmoc chemistry, Fmoc-L-Cys-(S^(t)Bu) is coupled to an appropriate resin, via one or more intermediate amino acids, and additional amino acids are thereafter coupled to the L-Cys-(S^(t)Bu) residue. S^(t)Bu may be employed with either L- or D-Cys, and any of a variety of other amino acids, including designer or unnatural amino acids and mimics thereof, characterized by an SH group available for binding to a metal ion, including, but not limited to, 3-mercapto phenylananine and other related 3-mercapto amino acids such as 3-mercapto valine (penicillamine); 2-mercaptoacetic acid; 3-mercaptopropionic acid; 2-mercaptopropionic acid; 3-mercapto-3,3,-dimethyl propionic acid; 3-mercapto,3-methyl propionic acid; 3-mercapto-3,3,-diethyl proprionic acid; 2-mercapto,2-methyl acetic acid; 3-cyclopentamethlene,3-mercaptopropionic acid; 2-cyclopentamethlene,2-mercaptoacetic acid and related amino acids. In all these cases, S-protection can be by S^(t)Bu, S-Acm, Mmt, Npys, S-sulfonate and related groups, as described above.

Metal Ion Complexation to MBD. The complexation of metal ions to the sequences in a library, and specifically to the MBD, is achieved by mixing the sequences with the metal ion. This is conveniently done in solution, with the solution including an appropriate buffer. In one approach, the metal ion is, when mixed with the peptide or peptidomimetic constituents, already in the oxidation state most preferred for complexing to the MBD. Some metal ions are complexed in their most stable oxidation state, such as calcium (II), potassium (I), indium (III), manganese (II), copper (II), zinc (II) and other metals. In other instances, the metal must be reduced to a lower oxidation state in order to be complexed to the MBD. This is true of ferrous, ferric, stannous, stannic, technetiumoxo[V], pertechnetate, rheniumoxo[V], perrhenate and other similar metal ions. Reduction may be performed prior to mixing with the sequences, simultaneously with mixing with the sequences, or subsequent to mixing with the sequences. Any means of reduction of metal ions to the desired oxidation state known to the art may be employed.

For tetradentate coordination with a metal ion, rhenium is a preferred ion. Solid phase resin bound peptide or peptidomimetic sequences may be labeled with rhenium ion by treatment with the rhenium transfer agent ReOCl₃(PPh₃)₂ in the presence of 1,8-Diazabicyclo[5,4,0] undec-7-ene as a base. The sequences may then be cleaved from the resin. Alternatively, peptide or peptidomimetic sequences in a soluble library may similarly be labeled by treatment with the rhenium transfer agent ReOCl₃(PPh₃)₂ in the presence of 1,8-Diazabicyclo[5,4,0] undec-7-ene as a base. Metal complexation in the presence of 1,8-Diazabicyclo[5,4,0]undec-7-ene (DBU) as a base can conveniently be accomplished at ambient room temperature.

In an alternative method of metal complexation a mild base, such as sodium acetate, can be used. In this case the thiol-containing sequence, either in solution or bound to solid phase, is taken in a suitable solvent, such as DMF, NMP, MeOH, DCM or a mixture thereof, and heated to 60-70° C. with the rhenium transfer agent ReOCl₃(PPh₃)₂ in the presence of sodium acetate for 15 minutes. Similarly, other bases such as triethylamine, ammonium hydroxide and so on, may be employed. According to this invention, MeOH is a preferred choice of solvent for rhenium complexation in the case of S-deprotected peptides in solution. The solvent choice for S-deprotected peptides still attached to the solid phase is guided mainly by considerations of superior solvation (swelling) of the solid phase. DMF and NMP may be employed. Various mixtures of these solvents, also in combination with MeOH, and DCM, CHCl₃ and so on, may also be employed to yield optimized complexation results.

In one embodiment of this invention, an S^(t)Bu protected peptide is treated in situ with rhenium transfer agent in the presence of DBU and tributylphosphine to effect S-deprotection and rhenium complexation in one pot. Alternately, complexation of rhenium to the S^(t)Bu protected peptide in the presence of rhenium perrhenate may be accomplished by treatment with Sn[II]Cl₂. This reagent effects S-deprotection as well as conversion of ReO₄ state to ReO state in situ to cause complexation of the rhenium to the S-deprotected peptide. A preferred procedure in this invention is the use of S^(t)Bu protected peptide with S-deprotection by treatment with tributylphosphine, and metal complexation of the resulting peptide utilizing ReOCl₃(PPh₃)₂ in the presence of DBU at room temperature.

In the libraries of this invention, the MBD forms a reverse turn structure upon complexation with a metal ion, with the library constructed such that side chains of amino acids within the MBD are varied, and similarly amino acids not forming a part of the MBD are also varied. Various compounds in a library of metallopeptides can be obtained by varying the sequence of amino acids in a set of peptides that are all optimized to form a complex of nearly similar geometry when coordinated with a metal ion. This optimization can be obtained, for example, by appropriate positioning of amino acids having high affinity to complex a metal ion. Examples of naturally occurring amino acids with high affinity for metal complexation include Cys and His. A library of such peptides, therefore, would have at least one of these amino acids that is suitably placed in the sequence, with this amino acid being common to all the molecules in the library, with this amino acid thus non-randomized.

A conceptual, generalized view of a solid phase library of metallopeptides that is constructed using local conformational restriction is:

where M is a metal ion, A₁ and A₂ are amino acid side chains forming parts of the reverse turn structure which is the BBD, and “Peptide Chain” denotes one or more amino acids. A similar library can also be constructed in which the components are soluble, and thus not bound to a resin.

Another embodiment of this invention provides for construction of a library with global conformational restriction. In this embodiment, the MBD can be held constant, and a randomized or selected series of sequences of amino acids or mimetics varied to form the library. This type of library encompasses metallopeptides in which a MBD is an isosteric replacement for a disulfide, lactam, lactone, thioether or thioester moiety in cyclic peptides. In these constructs a set MBD is introduced between two pre-selected ends of a linear peptide or peptidomimetic that contains the randomized or selected series of sequences of amino acids or mimetics under investigation. The general structure of a metallopeptide library of this type is:

Peptide Chain (Containing Biological Function Domain)˜Resin

where M is a metal ion and A₁ and A₂ are structural elements that may provide additional stability to metal complexation, or may modulate biological activity, such as determining the organ of clearance, or altering biodistribution patterns or pharmacokinetics. The “Peptide Chain” sequence may be randomly varied, thereby resulting in a random library, or may be directed in a predetermined fashion, based upon known characteristics of the target molecule.

One illustration of a globally-constrained metallopeptide library is a library of peptides wherein all the individual members of the library include a metal ion-binding domain and the library is directed specifically towards a family of melanocortin receptors. The general formula of this library of peptides, before complexation to a metal ion, is:

A₁-Aa₁-Aa₂-Aa₃-A₂˜Resin

where X is a fixed MBD including a plurality of amino acids, so that all of the valences of the metal ion are satisfied upon complexation of the metal ion with X, A₁ and A₂ each comprise from 0 to about 20 amino acids, and Aa₁, Aa₂ and Aa₃ each comprise one or more amino acids connected to X through an amide, thioether, thioester, ester, carbamate, or urethane bond, wherein each of Aa₁, Aa₂ and Aa₃ is varied. In this example, the MBD may include an OSPG. Other thiols in the sequence may optionally include S-protecting groups that are not orthogonal, such that the OSPG may be removed without removal of other S-protecting groups in the sequence.

For solid phase libraries the peptide constructs are attached to a resin, and the resin is omitted for soluble libraries. The functional equivalent of each these peptide libraries may also be obtained through the development of a library of non-amino acid building blocks so as to result in structural mimics of these peptides. The peptide bonds may be replaced by pseudopeptide bonds, such as thioamides, thioethers, substituted amines, carbanate, urethane, aliphatic moieties, and functionally similar constructs.

A peptide library is first assembled according to the sequence specification and degeneration, as described above, by well-known methods of peptide synthesis. These libraries can be synthesized as discreet, spatially addressable compounds in parallel synthesis, using split synthesis approaches, or by deconvolution techniques of soluble libraries. Using similar methods, a pseudopeptide, peptidomimetic or non-peptide library can be obtained. The non-peptide libraries may also optionally incorporate one of various tagging approaches that are well known to those skilled in the art. Both solid-phase and soluble libraries can be obtained in this manner. The entire library is then reacted with an appropriate metal-complexing agent to obtain the corresponding metal-coordinated library, comprising a similar class of predetermined structures. For example, to complex a peptide library with rheniumoxo metal ion, the peptide library can be treated with Re(O)Cl₃(PPh₃)₂ in the presence of sodium acetate. This procedure results in quantitative complexation of ReO with the peptide. In order to complex Zn, Co, Mn, Fe or Cu ions, the peptide library is treated with chloride or other suitable salts of these metal ions to yield the library of corresponding metal ions. Essentially, a variety of metal ions can be used to construct different metallopeptide libraries. One limiting factor in selection of the appropriate metal ion is the relative stability of a particular metal-peptide complex, related in large part to the metal-peptide binding constant or constants. It is well known in the art that some metal-peptide constructs are stable only within specified pH or other special conditions, or are easily oxidized in air. Some peptide-metal ion complexes, such as those with ReO, are stable in pure form and can be isolated and stored under normal storage conditions for a long period of time.

A metallopeptide library constructed according to this invention can be screened to identify one or more receptor-binding or pharmacologically-active melanocortin receptor-specific candidates by various techniques that have been reported in the prior art. Both soluble and solid phase libraries may be directly employed in these assays. These techniques include direct target binding approaches as described by Lam and coworkers (Lam K S et al: Nature 354:82-84, 1991; Lam K S et al: Nature 360:768, 1992), deconvolution and iterative re-synthesis approaches (Houghten R A et al: Proc Natl Acad Sci USA 82:5131-5135, 1985; Berg et al: J Am Chem Soc 111:8024-8026, 1989; Dooley C T et al: Science 266:2019-2022, 1994; Blondelle S E: Antimicrob Agents Chemother 38:2280-2286, 1994; Panilla C: Biopolymers 37:221-240, 1995), approaches using orthogonal pools of two co-synthesized libraries according to Tartar and coworkers (Deprez B et al: J Am Chem Soc 117: 5405-5406, 1995), positional scanning methods devised by Houghton and coworkers that eliminate iterative re-synthesis (Dooley C T et al: Life Sci 52:1509-1517, 1993; Pinilla C et al: Biotechniques 13:901-905, 1992; Pinilla C et al: Drug Dev Res 33:133-145, 1992), and a combination of the positional scanning method with split synthesis methods (Erb E et al: Proc Natl Acad Sci USA, 91:11422-11426, 1994).

Among these techniques, the deconvolution and iterative resynthesis approach, the approach involving orthogonal pools of two co-synthesized libraries, and the positional scanning method may be directly applied to soluble metallopeptide libraries to elucidate the structure of a “hit,” or peptide identified as a receptor-binding or pharmacologically-active candidate in the screening process. For solid phase libraries, other than spatially addressable parallel synthesis libraries, the structure of hits can be directly determined by various strategies well known to those skilled in the art. These include direct mass spectrometric analysis of compounds covalently bound to solid phase matrix of particles by the use of matrix-assisted laser desorption/ionization (MALDI) techniques (Siuzdak G et al: Bioorg Med Chem Lett 6:979, 1996; Brown B B et al: Molecular Diversity 1:4-12, 1995). The technique of creating a series of partially end-capped compounds at each of the synthetic steps during library assembly also helps in unambiguous identification by mass spectrometry (Youngquist R S et al: J Am Chem Soc, 117:3900-3906, 1995; Youngquist R S et al: Rapid Commun Mass Spectr 8:77-81, 1994). In addition to these analytical techniques, various encoding strategies that have been devised for structure elucidation in organic molecule-based libraries, including non-peptide and non-nucleotide libraries, may be utilized. Various encoding strategies, such as DNA encoding, peptide encoding, haloaromatic tag encoding, and encoding based on radiofrequency transponders, are now well known in the art and can be used directly in combination with metallopeptide libraries. These tagging strategies require the incorporation of the tags during the course of synthesis of libraries, which can be accomplished during the construction of metallopeptide libraries, since metal complexation is a final, post-synthesis step.

Structural Diversity of Melanocortin Receptor-Specific Library Members. Examples of some of the molecular templates which may be employed in this invention are shown below for tetradentate metal ion complexation. In general, these molecular templates define groups of metallopeptides of this invention which, by substitution as provided, give rise to libraries of metallopeptides for use in determining melanocortin receptor-specific compounds, which may be either agonist or antagonist compounds. The templates are provided without the metal ion, it being understood that the compounds exhibit enhanced specificity for melanocortin receptors only upon metal ion complexation. R₁-Lll-Aaa-Bbb-Ccc-R₂  Template 1 and R₁-Bbb-Aaa-Ccc-R₂  Template 2

Where R₁ is any functionality that potentiates the intrinsic activity of the remainder of the molecule, including but not limited to providing an auxiliary or secondary receptor contact. Any of a variety of amino acids and non-peptide groups may be employed, including an amino acid chain from one to about four neutral or charged L- or D-configuration amino acid residues. If R₁ is a non-peptide group, it may be a linear or branched alkyl, aryl, alkene, alkenyl or aralkyl chain.

Where Aaa is an L- or D-configuration cationic amino acid with a positively charged side chain. Preferred amino acids include L-configuration Lys, Arg, Orn, Dpr or Dbu, and derivatives, analogs or homologs thereof, including both natural and synthetic amino acids. Aaa provides an N (nitrogen atom) for metal ion complexation.

Where Bbb is an L- or D-configuration amino acid with an aromatic side chain. Preferred amino acids include D-configuration Phe, Phe(4′Cl), Phe(3′,4′ Di-Cl), Phe(4′-nitro), Phe(4′-methyl), Phe(4′-Phenyl), Hphe, Pgl, Trp, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl), Cys(Bzl), or Tyr(BzlCl₂), and derivatives, analogs or homologs thereof. The aromatic ring in Bbb may be functionalized with halogen, alkyl or aryl groups. Bbb provides an N for metal ion complexation.

Where Ccc is an amino acid that provides both an N, from the alpha amino group, and an S (sulfur atom), from a side chain group, for metal ion complexation. Preferred amino acids include L- or D-configuration Cys, Pen and Hcys.

Where Lll is a D-configuration amino acid with an aromatic side chain. Preferred amino acids include D-configuration Phe, Phe(4′Cl), Phe(3′,4′ Di-Cl), Phe(4′-nitro), Phe(4′-methyl), Phe(4′-Phenyl), Hphe, Pgl, Trp, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl), Cys(Bzl), or Tyr(BzlCl₂), and derivatives, analogs or homologs thereof. The aromatic ring in Lll may be functionalized with halogen, alkyl or aryl groups. Lll does not provide an N for metal ion complexation.

Where R₂ is an amino acid with an aromatic side chain. Preferred amino acids include L- or D-configuration Phe, Trp, Phe(4′Cl), Phe(3′,4′ Di-Cl), Phe(4′-nitro), Phe(4′-methyl), Phe(4′-Phenyl), Hphe, Pgl, Trp, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl), Cys(Bzl) or Tyr(BzlCl₂), and derivatives, analogs or homologs thereof, including both natural and synthetic amino acids. The C-terminus may be free or amidated. R₂ may also be the corresponding des-carboxylamino acid of any of the foregoing. Alternatively, R₂ may be eliminated.

FIG. 1 depicts the structure of Template 1, and FIG. 2 depicts the structure of Template 2, in both cases showing coordination with a tetradenate coordination sphere metal ion, resulting in an N₃ μl metal ion bond. R₁-Ddd-Bbb-Aaa-R₃  Template 3

Where R₁, Bbb and Aaa are as described above.

Where Ddd is an amino acid that provides an S, from a side chain group, for metal ion complexation. Preferred amino acids include L- or D-configuration Cys, Pen and Hcys.

Where R₃ is an amino acid with an aromatic side chain that provides an N for metal ion complexation. Preferred amino acids include L- or D-configuration Phe, Trp, Phe(4′Cl), Phe(3′,4′ Di-Cl), Phe(4′-nitro), Phe(4′-methyl), Phe(4′-Phenyl), Hphe, Pgl, Trp, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl), Cys(Bzl) or Tyr(BzlCl₂), and derivatives, analogs or homologs thereof, including both natural and synthetic amino acids. The C-terminus may be free or amidated. R₃ may also be the corresponding des-carboxylamino acid of any of the foregoing.

FIG. 3 depicts the structure of Template 3, showing coordination with a tetradenate coordination sphere metal ion, resulting in an N₃S₁ metal ion bond. R₄-Eee-Bbb-Ccc-R₂  Template 4

Where R₂, Bbb and Ccc are as described above.

Where R₄ is a functionality that provides a cationic center. Preferred amino acids include L- or D-configuration Lys, Arg, Orn, Dpr or Dbu, and derivatives, analogs or homologs thereof, including both natural and synthetic amino acids. The N-terminus of the amino acid may be functionalized with any of a variety of neutral amino acid and non-peptide groups, including linear or branched alkyl, aryl, alkene, alkenyl or aralkyl chains.

Where Eee is an uncharged L- or D-configuration amino acid that provides an N for metal ion complexation. Preferred amino acids include Gly and L-configuration Ala, Nle, Leu, Val, Phe or Trp, and derivatives, analogs or homologs thereof, including both natural and synthetic amino acids. In a preferred embodiment, Eee isn an amino acid with an aliphatic side chain.

FIG. 4 depicts the structure of Template 4, showing coordination with a tetradenate coordination sphere metal ion, resulting in an N₃S₁ metal ion bond. R₁-Fff-Aaa-Ggg-Ccc-R₅  Template 5

Where R₁, Aaa and Ccc are as described above.

Where Fff is an L- or D-configuration aromatic amino acid. Preferred amino acids include D-configuration Phe, Phe(4′Cl), Phe(3′,4′ Di-Cl), Phe(4′-nitro), Phe(4′-methyl), Phe(4′-Phenyl), Hphe, Pgl, Trp, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl), Cys(Bzl), Tyr(BzlCl₂), Tic, Tiq or Tca, and derivatives, analogs or homologs thereof, including both natural and synthetic amino acids. The aromatic ring in Fff may be substituted with halogen, alkyl or aryl groups. Fff does not provide an N for metal ion complexation.

Where Ggg is an L- or D-configuration aromatic amino acid. Preferred amino acids include L-configuration Phe, Phe(4′Cl), Phe(3′,4′ Di-Cl), Phe(4′-nitro), Phe(4′-methyl), Phe(4′-Phenyl), Hphe, Pgl, Trp, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl), Cys(Bzl) or Tyr(BzlCl₂), and derivatives, analogs or homologs thereof, including both natural and synthetic amino acids. The aromatic ring in Ggg may be substituted with halogen, alkyl or aryl groups. Ggg provides an N for metal ion complexation.

Where R₅ is preferably an amide, substituted amide, ester or carboxylate group. R₅ may also be and L- or D-configuration amino acid or amino acid amide, including an aromatic, aliphatic, neutral or charged amino acid.

FIG. 5 depicts the structure of Template 5, showing coordination with a tetradenate coordination sphere metal ion, resulting in an N₃S₁ metal ion bond. R₁-Hhh-Aaa-Bbb-Ccc-R₅  Template 6

Where R₁, Aaa, Bbb, Ccc and R₂ are as described above.

Where Hhh is an L- or D-configuration cationic amino acid with a positively charged side chain. Preferred amino acids include L-configuration Lys, Arg, Orn, Dpr or Dbu, and derivatives, analogs or homologs thereof, including both natural and synthetic amino acids. Hhh does not provide an N for metal ion complexation.

FIG. 6 depicts the structure of Template 6, showing coordination with a tetradenate coordination sphere metal ion, resulting in an N₃S₁ metal ion bond. R₁-Iii-Iii-Ccc-Jjj-Kkk-R₂  Template 7

Where R₁, Ccc and R₂ are as described above.

Where Iii is an L- or D-configuration amino acid that provides an N for metal ion complexation. Preferred amino acids includes Ala, Gly, Nle, Val, Leu, Ile, His, Lys, or Arg, and derivatives, analogs or homologs thereof, including both natural and synthetic amino acids.

Where Jjj is an L- or D-configuration amino acid with an aromatic side chain. Preferred amino acids include D-configuration Phe, Phe(4′Cl), Phe(3′,4′ Di-Cl), Phe(4′-nitro), Phe(4′-methyl), Phe(4′-Phenyl), Hphe, Pgl, Trp, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl), Cys(Bzl), or Tyr(BzlCl₂), and derivatives, analogs or homologs thereof. The aromatic ring in Jjj may be functionalized with halogens, alkyl or aryl groups. Jjj does not provide an N for metal ion complexation.

Where Kkk is an L- or D-configuration cationic amino acid with a positively charged side chain. Preferred amino acids include L-configuration Lys, Arg, Orn, Dpr or Dbu, and derivatives, analogs or homologs thereof, including both natural and synthetic amino acids. Aaa does not provide an N for metal ion complexation.

FIG. 7 depicts the structure of Template 7, showing coordination with a tetradenate coordination sphere metal ion, resulting in an N₃S₁ metal ion bond.

The foregoing templates may be employed with tetradentate coordination sphere metal ions, such as various forms of technetium and rhenium. Corresponding templates may be constructed for use with metal ions of other coordination spheres.

Representative Peptides of this Invention. Representative peptides of this invention were made using library and synthesis methods described herein, and selected peptides were tested using a binding assay. Table 1 sets forth peptides of this invention, and the results of competitive inhibition binding assays. The peptides were synthesized using conventional peptide synthesis methods, and were complexed with rhenium using the methods described herein.

The competitive inhibition binding assay was conducted using membranes prepared from hMC4-R and B-16 mouse melanoma cells (containing MC1-R) using 0.4 nM ¹²⁵I-NDP-α-MSH (New England Nuclear, Boston, Mass., USA) in 50 mM HEPES buffer containing 1 mM MgCl₂, 2 mM CaCl₂, and 5 mM KCl, at pH 7.2. The assay tube also contained a chosen concentration of the test peptide of this invention, complexed to a rhenium metal ion as indicated, for determining its efficacy in inhibiting the binding of ¹²⁵I-NDP-α-MSH to its receptor. Non-specific binding was measured by complete inhibition of binding of ¹²⁵I-NDP-α-MSH in the assay with the presence of 1 μM α-MSH. Incubation was for 90 minutes at room temperature, after which the assay mixture was filtered and the membranes washed three times with ice cold buffer. The filter was dried and counted in a gamma counter for remaining radioactivity bound to the membranes. 100% specific binding was defined as the difference in radioactivity (cpm) bound to cell membranes in the absence and presence of 1 μM α-MSH. The cpm obtained in presence of test compounds were normalized with respect to 100% specific binding to determine the percent inhibition of ¹²⁵I-NDP-α-MSH binding. Each assay was conducted in triplicate and the actual mean valves are described in Table 1. Negative numbers in Table 1 under “% Inhibition” result from experimental variance, and are indicative of no inhibition; similarly, values over 100% also result from experimental variance, and are indicative of complete inhibition. TABLE 1 Melanocortin Receptor Screening Results: Receptor Binding Assay Ion/ Conc. % Inhibition Linear Cut off MC1-R ID peptide Sequence Structure (μM) MC4-R (B-16) PL-808 ReO[V] Ac-L-His-L-Trp-L-Cys-L-Trp-NH₂ (SEQ ID NO: 3) 1 0 −3 PL-809 ReO[V] Ac-L-His-L-Hphe-L-Cys-L-Trp-NH₂ (SEQ ID NO: 4) 1 0 −4 PL-810 ReO[V] Ac-L-His-L-Nal 2-L-Cys-L-Trp-NH₂ (SEQ ID NO: 5) 1 −1 −2 PL-811 ReO[V] Ac-L-His-L-Phg-L-Cys-L-Trp-NH₂ (SEQ ID NO: 6) 1 0 −5 PL-812 Linear Ac-L-His-L-Phe-L-Cys-L-Trp-NH₂ (SEQ ID NO: 7) 10 29 54 PL-813 Linear Ac-L-His-D-Phe-L-Cys-L-Trp-NH₂ 10 8 91 PL-814 ReO[V] Ac-L-His-L-Phe-L-Cys-L-Trp-NH₂ (SEQ ID NO: 7) 1 0 −4 PL-815 ReO[V] Ac-L-His-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 10 7 93 PL-816 ReO[V] Ac-L-His-D-Phe-L-Cys-L-Trp-NH₂ 10 28 70 PL-836 ReO[V] Ac-L-His-L-Phe-D-Arg-L-Cys-L-Trp-NH₂ 10 26 78 PL-837 ReO[V] Ac-L-His-D-Phe-D-Arg-L-Cys-L-Trp-NH₂ 10 0 54 PL-838 ReO[V] Ac-L-His-L-Phe-L-Arg-L-Cys-L-Trp-NH₂ (SEQ ID 10 0 35 NO: 8) PL-839 ReO[V] Ac-L-His-L-Phe-L-Trp-L-Cys-NH₂ (SEQ ID NO: 9) 10 9 12 PL-840 ReO[V] Ac-L-His-L-Phe-D-Trp-L-Cys-NH₂ 10 10 8 PL-841 ReO[V] Ac-L-His-D-Phe-D-Trp-L-Cys-NH₂ 10 0 19 PL-842 ReO[V] Ac-L-His-D-Phe-L-Trp-L-Cys-NH₂ 10 2 4 PL-843 ReO[V] Ac-D-Phe-Gly-L-Cys-L-Trp-NH₂ 10 1 10 PL-844 ReO[V] Ac-L-Phe-Gly-L-Cys-L-Trp-NH₂ (SEQ ID NO: 10) 10 2 10 PL-845 ReO[V] Ac-D-Phe-L-His-Gly-L-Cys-L-Trp-NH₂ 10 0 5 PL-846 ReO[V] Ac-L-Phe-D-His-Gly-L-Cys-L-Trp-NH₂ 10 0 2 PL-847 ReO[V] Ac-L-Phe-L-His-Gly-L-Cys-L-Trp-NH₂ (SEQ ID 10 6 −6 NO: 11) PL-848 ReO[V] Ac-D-Phe-D-His-Gly-L-Cys-L-Trp-NH₂ 10 10 19 PL-989 ReO[V] Bz-D-Tyr-L-Nal-L-Cys-L-Phe-NH₂ 10 11 35 PL-997 ReO[V] Bz-D-Nal-L-Tyr-L-Cys-L-Phe-NH₂ 10 36 6 PL-1073 ReO[V] Ac-L-Ala-L-Tle-L-Cys-L-Trp-NH₂ (SEQ ID NO: 12) 1 13 −6 PL-1089 ReO[V] Ac-L-Ala-L-pF-Phe-L-Cys-L-Trp-NH₂ (SEQ ID 10 10 0 NO: 13) PL-1090 ReO[V] Ac-L-Ala-L-Tyr(3′,5′ di-I, 4′-Ac)-L-Cys-L-Trp-NH₂ 1 10 2 (SEQ ID NO: 14) PL-1091 ReO[V] BAla-Gly-L-Cys(Bzl)-L-Cys-L-Trp-NH₂ (SEQ ID 1 13 −1 NO: 15) PL-1092 ReO[V] BAla-Gly-L-Lys(TFA)-L-Cys-L-Trp-NH₂ (SEQ ID 1 4 4 NO: 16) PL-1093 ReO[V] BAla-Gly-L-Phe(2,4-di Cl)-L-Cys-L-Trp-NH₂ (SEQ ID 1 2 2 NO: 17) PL-1094 ReO[V] BAla-Gly-L-Phe(2-Cl)-L-Cys-L-Trp-NH₂ (SEQ ID 10 19 57 NO: 18) PL-1095 ReO[V] BAla-Gly-L-Lys(Z)-L-Cys-L-Trp-NH₂ (SEQ ID NO: 19) 10 8 3 PL-1096 ReO[V] BAla-Gly-L-Leu-L-Cys-L-Trp-NH₂ (SEQ ID NO: 20) 10 12 6 PL-1102 ReO[V] BAla-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 60 9 PL-1103 ReO[V] BAla-Gly-D-Phg-L-Cys-L-Trp-NH₂ 10 12 −3 PL-1109 ReO[V] L-Lys-L-His-D-Phe-L-Cys-L-Trp-NH₂ 10 37 73 PL-1110 ReO[V] L-Lys-L-His-L-Phe-L-Cys-L-Trp-NH₂ (SEQ ID NO: 21) 10 36 11 PL-1111 ReO[V] L-His-D-Phe-L-Cys-L-Trp-NH₂ 10 0 0 PL-1112 ReO[V] L-His-L-Phe-L-Cys-L-Trp-NH₂ (SEQ ID NO: 7) 10 8 0 PL-1113 ReO[V] BAla-L-His-D-Phe-L-Cys-L-Trp-NH₂ 10 31 82 PL-1114 ReO[V] BAla-L-His-L-Phe-L-Cys-L-Trp-NH₂ (SEQ ID NO: 22) 10 10 2 PL-1140 ReO[V] Ac-D-Phe-Arg-L-Cys-L-Phe-NH₂ 10 12 62 PL-1141 ReO[V] Ac-D-Phe-Arg-L-Cys-L-Trp-NH₂ 10 11 57 PL-1144 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Phe-L-Arg-L-Cys-L-Phe-NH₂ 1 14 99 PL-1145 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 1 17 96 PL-1146 ReO[V] Ac-D-Phe-Gly-L-Cys-L-Phe-NH₂ 10 9 39 PL-1147 ReO[V] Ac-D-Pip-Gly-L-Cys-L-Phe-NH₂ 10 12 40 PL-1156 ReO[V] Ac-D-Phe-L-Tle-L-Cys-L-Trp-NH₂ 10 14 −19 PL-1157 ReO[V] Ac-L-Nle-L-Arg-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 92 53 PL-1158 ReO[V] BAla-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 10 62 0 PL-1159 ReO[V] BAla-L-His-D-Nal 2-L-Cys-L-Trp-NH₂ 10 63 67 PL-1160 ReO[V] BAla-L-Phe-D-Nal 2-L-Cys-L-Trp-NH₂ 10 66 1 PL-1161 ReO[V] BAla-L-Nal 2-D-Nal 2-L-Cys-L-Trp-NH₂ 10 64 3 PL-1162 ReO[V] Heptanoyl-L-Arg-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 79 64 PL-1163 ReO[V] BAla-D-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 10 51 4 PL-1164 ReO[V] BAla-D-His-D-Nal 2-L-Cys-L-Trp-NH₂ 10 42 2 PL-1165 ReO[V] BAla-D-Phe-D-Nal 2-L-Cys-L-Trp-NH₂ 10 43 7 PL-1166 ReO[V] BAla-D-Nal 2-D-Nal 2-L-Cys-L-Trp-NH₂ 10 44 5 PL-1167 ReO[V] Abu-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 31 −1 PL-1168 ReO[V] 6-Axh-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 41 −2 PL-1169 ReO[V] 8-Aoc-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 41 −3 PL-1170 ReO[V] 11-Aun-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 27 9 PL-1171 ReO[V] 12-Ado-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 29 −5 PL-1172 ReO[V] Ac-L-Arg-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 58 −7 PL-1173 ReO[V] Ac-L-Lys-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 41 −2 PL-1174 ReO[V] Ac-L-Orn-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 53 −2 PL-1175 ReO[V] Ac-L-Nle-L-Arg-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 96 88 PL-1176 ReO[V] 7-Ahept-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 40 −8 PL-1177 ReO[V] B-Gpa-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 48 −6 PL-1178 ReO[V] Ac-L-Nle-L-Ala-L-His-D-HPhe-L-Arg-L-Cys-L-Trp- 1 4 51 NH₂ PL-1179 ReO[V] Ac-L-Nle-L-Ala-L-His-D-His-L-Arg-L-Cys-L-Trp-NH₂ 1 21 −5 PL-1180 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Trp-L-Arg-L-Cys-L-Trp-NH₂ 1 24 86 PL-1181 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Tyr-L-Arg-L-Cys-L-Trp-NH₂ 1 27 86 PL-1183 ReO[V] Ac-L-Nle-L-Ala-L-Arg-D-Nal 2-L-Arg-L-Cys-L-Trp- 1 82 96 NH₂ PL-1184 ReO[V] Ac-L-Nle-L-Ala-L-Tyr-D-Nal 2-L-Arg-L-Cys-L-Trp-NH₂ 1 58 36 PL-1185 ReO[V] Ac-L-Nle-L-Ala-L-Phe-D-Nal 2-L-Arg-L-Cys-L-Trp- 1 35 52 NH₂ PL-1186 ReO[V] Ac-L-Nle-L-Ala-L-Trp-D-Nal 2-L-Arg-L-Cys-L-Trp- 1 35 17 NH₂ PL-1187 ReO[V] Ac-L-Ala-L-His-D-Nal 2-L-Arg-L-Cys-L-Trp-NH₂ 1 48 58 PL-1188 ReO[V] Ac-L-Nle-L-Ala-D-Trp-D-Nal 2-L-Arg-L-Cys-L-Trp- 1 38 −12 NH₂ PL-1189 ReO[V] Ac-L-Nle-L-Ala-D-Phe-D-Nal 2-L-Arg-L-Cys-L-Trp- 1 36 −15 NH₂ PL-1190 ReO[V] Ac-L-Nle-L-Ala-D-His-D-Nal 2-L-Arg-L-Cys-L-Trp- 1 31 17 NH₂ PL-1191 ReO[V] Ac-L-Nle-L-Ala-D-Arg-D-Nal 2-L-Arg-L-Cys-L-Trp- 1 41 38 NH₂ PL-1192 ReO[V] Ac-L-Nle-L-Ala-D-Tyr-D-Nal 2-L-Arg-L-Cys-L-Tyr- 1 26 −5 NH₂ PL-1193 ReO[V] Ac-L-Glu-L-Ala-D-Nal 2-L-Arg-L-Cys-L-Trp-NH₂ 1 29 51 PL-1194 ReO[V] HOOC—(CH₂)₃—CO-L-His-D-Nal 2-L-Arg-L-Cys-L-Trp- 1 −3 23 NH₂ PL-1195 ReO[V] Ac-L-Ala-L-Glu-L-His-D-Nal 2-L-Arg-L-Cys-L-Trp- 1 9 45 NH₂ PL-1196 ReO[V] Ac-L-Nle-L-Glu-L-His-D-Nal 2-L-Arg-L-Cys-L-Trp- 1 31 89 NH₂ PL-1197 ReO[V] Ac-L-Glu-L-His-D-Nal 2-L-Arg-L-Cys-L-Trp-NH₂ 1 9 44 PL-1198 ReO[V] Ac-L-Glu-L-His-D-Nal 2-L-Cys-L-Arg-NH₂ 1 4 −5 PL-1199 ReO[V] Ac-L-Glu-L-His-L-Cys-D-Nal 2-L-Arg-NH₂ 1 1 −11 PL-1200 ReO[V] Ac-L-Glu-L-His-D-Nal 2-L-Cys-L-Arg-L-Trp-NH₂ 1 10 8 PL-1201 ReO[V] Ac-L-Glu-L-His-L-Cys-D-Nal 2-L-Arg-L-Trp-NH₂ 1 65 −7 PL-1202 ReO[V] Ac-L-Nle-L-Ala-D-Trp-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 1 17 10 PL-1203 ReO[V] Ac-L-Nle-L-Ala-D-Nal 2-D-Nal 2-L-Arg-L-Cys-L-Trp- 1 35 4 NH₂ PL-1204 ReO[V] Ac-L-Nle-L-Ala-D-Nal 1-D-Nal 2-L-Arg-L-Cys-L-Trp- 1 32 0 NH₂ PL-1205 ReO[V] Ac-L-Nle-L-Ala-Gly-D-Nal 2-L-Arg-L-Cys-L-Trp-NH₂ 1 54 60 PL-1206 ReO[V] Heptanoyl-D-Trp-D-Nal 2-L-Arg-L-Cys-L-Trp-NH₂ 1 17 0 PL-1207 ReO[V] Ac-L-Ala-L-His-D-Nal 2-L-Cys-D-Nal 2-L-Arg-L-Trp- 1 84 26 NH₂ PL-1209 ReO[V] Ac-L-Nal 2-L-His-D-Nal 2-L-Cys-D-Nal 2-L-Arg-L- 1 77 1 Trp-NH₂ PL-1210 ReO[V] Ac-D-Nal 2-L-His-D-Nal 2-L-Cys-D-Nal 2-L-Arg-L- 1 71 0 Trp-NH₂ PL-1211 ReO[V] Heptanoyl-L-Glu-L-His-D-Nal 2-L-Cys-D-Nal 2-L-Arg- 1 67 26 L-Trp-NH₂ PL-1212 ReO[V] Ac-L-Glu-D-Trp-D-Nal 2-L-Cys-D-Nal 2-L-Arg-L-Trp- 1 80 0 NH₂ PL-1213 ReO[V] Ac-D-Trp-D-Arg-L-Nal 2-D-Nal 2-L-Cys-D-Nal 2-L- 1 94 34 Arg-L-Trp-NH₂ PL-1214 ReO[V] Heptanoyl-L-Arg-Gly-D-Nal 2-D-Nal 2-L-Cys-D-Nal 1 78 47 2-L-Arg-L-Trp-NH₂ PL-1215 ReO[V] Gly-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 31 20 PL-1216 ReO[V] L-Lys-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 47 0 PL-1217 ReO[V] L-Lys(Z)-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 52 24 PL-1218 ReO[V] BAla-L-Arg(Tos)-D-Nal 2-L-Cys-L-Trp-NH₂ 10 57 1 PL-1220 ReO[V] BAla-L-Tle-D-Nal 2-L-Cys-L-Trp-NH₂ 10 69 30 PL-1221 ReO[V] BAla-L-Tyr(BzlDiCl 2,6)-D-Nal 2-L-Cys-L-Trp-NH₂ 10 35 37 PL-1222 ReO[V] BAla-Gly-D-Phe-L-CysL-Trp-NH₂ 10 27 9 PL-1223 ReO[V] Ac-L-Nle-L-Arg-D-Phe-D-Nal 2-L-Cys-L-Trp-NH₂ 10 64 79 PL-1225 ReO[V] GBzA-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 12 0 PL-1226 ReO[V] AVA-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 19 0 PL-1227 ReO[V] 2-Abz-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 5 0 PL-1228 ReO[V] BAla-L-His-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 11 64 PL-1229 ReO[V] BAla-L-Nle-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 32 21 PL-1230 ReO[V] GAA-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 32 20 PL-1231 ReO[V] GVA(Cl)-Gly-D-Nal 2-L-Cys-L-Trp-NH₂ 10 32 28 PL-1232 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 1 90 49 PL-1233 ReO[V] BAla-L-Arg-D-Nal 2-L-Cys-L-Trp-NH₂ 10 94 100 PL-1234 ReO[V] BAla-D-Arg-D-Nal 2-L-Cys-L-Trp-NH₂ 10 83 84 PL-1235 ReO[V] Heptanoyl-L-Arg-D-Nal 2-L-Cys-L-Trp-NH₂ 10 96 100 PL-1236 ReO[V] Heptanoyl-D-Arg-D-Nal 2-L-Cys-L-Trp-NH₂ 10 54 70 PL-1237 ReO[V] BAla-Gly-D-Lys(Z)-L-Cys-L-Trp-NH₂ 10 26 86 PL-1238 ReO[V] BAla-Gly-D-Tyr(Bzl)-L-Cys-L-Trp-NH₂ 10 40 40 PL-1239 ReO[V] BAla-Gly-D-Phe(DiF 3,4)-L-Cys-L-Trp-NH₂ 10 20 18 PL-1240 ReO[V] BAla-Gly-D-Val-L-Cys-L-Trp-NH₂ 10 13 0 PL-1241 ReO[V] BAla-Gly-D-Nal 1-L-Cys-L-Trp-NH₂ 10 34 23 PL-1242 ReO[V] D-Nal 2-Gly-L-Arg-L-Cys-L-Trp-NH₂ 10 61 80 PL-1243 ReO[V] D-Nal 2-Gly-D-Arg-L-Cys-L-Trp-NH₂ 10 62 88 PL-1244 ReO[V] D-Phe-Gly-L-Arg-L-Cys-L-Trp-NH₂ 10 46 69 PL-1245 ReO[V] D-Phe-Gly-D-Arg-L-Cys-L-Trp-NH₂ 10 50 74 PL-1248 ReO[V] Ac-L-Nle-D-Arg-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 10 69 63 PL-1249 ReO[V] BAla-L-Nle-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 10 64 40 PL-1250 ReO[V] BAla-D-Nle-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 1 79 10 PL-1251 ReO[V] Ac-L-Nle-L-Arg-L-Phe-D-Nal 2-L-Cys-L-Trp-NH₂ 1 82 77 PL-1252 ReO[V] D-Lys(Z)-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 10 44 34 PL-1253 ReO[V] L-Ala-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 10 54 27 PL-1254 ReO[V] L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 10 40 43 PL-1255 ReO[V] Bz-L-Arg-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 1 85 14 PL-1256 ReO[V] L-Arg-D-Nal 2-L-Cys-L-Trp-NH₂ 10 60 57 PL-1257 ReO[V] HOOC(CH₂)₂—CO-L-Arg-D-Nal 2-L-Cys-L-Trp-NH₂ 10 51 43 PL-1258 ReO[V] BAla-L-Nle-D-Nal 2-L-Cys-L-Trp-NH₂ 10 66 57 PL-1259 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Phe-L-Arg-L-Cys-NH₂ 1 31 82 PL-1260 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Nal 2-L-Cys-NH₂ 1 74 49 PL-1261 ReO[V] Heptanoyl-L-His-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 1 30 101 PL-1262 ReO[V] Heptanoyl-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 1 20 44 PL-1263 ReO[V] Ac-L-Arg(Tos)-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 1 26 33 PL-1264 ReO[V] Ac-L-Nle-L-Glu-L-His-D-Nal 2-L-Arg-L-Trp-L-Cys- 0.1 54 45 NH₂ PL-1265 ReO[V] Ac-L-Glu-L-His-Gly-L-Arg-L-Trp-L-Cys-NH₂ (SEQ ID 1 67 34 NO: 23) PL-1266 ReO[V] Ac-L-Nle-L-Ala-D-Trp-D-Nal 2-L-Arg-L-Trp-L-Cys- 1 87 30 NH₂ PL-1267 ReO[V] Admentoyl-Gly-D-Nal 2-L-Arg-L-Trp-L-Cys-NH₂ 1 55 36 PL-1268 ReO[V] Bz-L-His-Gly-D--Nal 2-L-Arg-L-Trp-L-Cys-NH₂ 1 97 57 PL-1269 ReO[V] Bz-L-His-L-Cys-D-Nal 2-L-Arg-L-Trp-NH₂ 1 99 25 PL-1270 Linear Ac-L-Nle-L-Ala-L-His-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 1 57 101 PL-1271 ReO[V] Ac-D-Trp-D-Arg-L-Nal 2-L-Cys-D-His-L-Nal 2-NH₂ 1 32 35 PL-1272 Linear Heptanoyl-L-His-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 1 36 100 PL-1273 ReO[V] Ac-L-Nle-L-Arg-D-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 10 53 78 PL-1274 ReO[V] Ac-L-Nle-L-Arg-D-Phe-D-Nal 2-L-Cys-L-Trp-NH₂ 10 45 75 PL-1275 ReO[V] Des-aminoTyr-L-Lys-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 1 17 −4 PL-1276 ReO[V] Heptanoyl-L-Lys-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 1 64 4 PL-1277 ReO[V] 3-Pyridine propionyl-L-Lys-L-Ala-D-Nal 2-L-Cys-L- 1 38 −17 Trp-NH₂ PL-1278 ReO[V] EtOOC—(CH₂)₄—CO-L-Lys-L-Ala-D-Nal 2-L-Cys-L-Trp- 1 32 −13 NH₂ PL-1279 ReO[V] (s)-2-OH-isocaproyl--L-Lys-L-Phe-D-Nal 2-L-Cys-L- 1 55 −10 Trp-NH₂ PL-1280 ReO[V] 4-MePhenoxyacetyl--L-Lys-L-Ala-D-Nal 2-L-Cys-L- 1 49 −11 Trp-NH₂ PL-1281 ReO[V] Heptanoyl-L-Lys-L-Ala-D-Phe-L-Cys-L-Trp-NH₂ 1 29 60 PL-1282 ReO[V] Heptanoyl-L-Lys-L-Ala-D-Phe-D-Cys-L-Trp-NH₂ 1 14 −30 PL-1283 ReO[V] Des-aminoPhe-L-Lys-L-Ala-D-Nal 2-L-Cys-L-Trp- 1 45 −20 NH₂ PL-1284 ReO[V] BAla-L-Lys(Ac)-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 1 27 −26 PL-1285 ReO[V] Ac-L-Nle-L-Ala-D-Trp-D-Phe-L-Arg-L-Trp-L-Cys-NH₂ 1 32 54 PL-1286 ReO[V] Ac-L-Nle-L-Ala-D-Nal 2-D-Phe-L-Arg-L-Trp-L-Cys- 1 34 7 NH₂ PL-1287 ReO[V] Ac-L-Nle-L-Ala-D-His-D-Phe-L-Arg-L-Trp-L-Cys-NH₂ 1 40 62 PL-1288 ReO[V] EtOOC—(CH₂)₄—CO-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 1 16 −3 PL-1289 ReO[V] 4-n-Heptanoyl-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 1 31 −7 PL-1290 ReO[V] Des-aminoTyr-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 1 24 −22 PL-1291 ReO[V] Me2-CH—CH(L-OH)—CO-D-Phe-L-Arg-L-Cys-L-Trp- 1 29 1 NH₂ PL-1292 ReO[V] Ac-D-Ala-L-HisL-Cys-D-Nal 2-L-Arg-Tryptamide 1 87 25 PL-1293 ReO[V] Ac-D-Ala-L-HisL-Cys-D-Nal 2-L-Arg-Tryptamide 1 96 21 PL-1294 ReO[V] Bz-L-His-L-Cys-D-Phe-L-Arg-L-Trp-NH₂ 1 65 62 PL-1295 ReO[V] Bz-L-Ala-L-Cys-D-Phe-L-Arg-L-Trp-NH₂ 1 72 62 PL-1296 ReO[V] Bz-L-Nal 2-L-Cys-D-Phe-L-Arg-L-Trp-NH₂ 1 51 51 PL-1297 ReO[V] Des-aminoPhe-L-Cys-D-Nal 2-L-Arg-L-Trp-NH₂ 1 91 31 PL-1298 ReO[V] Heptanoyl-L-Cys-D-Nal 2-L-Arg-L-Trp-NH₂ 1 95 43 PL-1299 ReO[V] Heptanoyl-BAla-L-Arg-L-Cys-L-Trp-NH₂ (SEQ ID 1 19 1 NO: 24) PL-1300 ReO[V] Heptanoyl-L-Ala-L-Arg-L-Cys-L-Trp-NH₂ (SEQ ID 1 22 62 NO: 25) PL-1301 ReO[V] L-Lys(Z)-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 1 72 49 PL-1302 ReO[V] Heptanoyl-L-His-D-Phe-L-Arg-D-Cys-L-Trp-NH₂ 1 24 77 PL-1303 ReO[V] Heptanoyl-L-His-D-Nal 2-L-Arg-D-CysL-Trp-NH₂ 1 60 39 PL-1304 ReO[V] D-Lys(Z)-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 1 42 −10 PL-1305 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 1 91 14 PL-1306 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe-L-Cys-L-Trp-NH₂ 1 36 56 PL-1309 ReO[V] Heptanoyl-L-Cys-L-Arg-L-Cys-L-Trp-NH₂ (SEQ ID 1 10 9 NO: 26) PL-1310 ReO[V] Des-aminoTyr-L-Lys-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 10 78 100 PL-1311 ReO[V] Heptanoyl-L-Lys-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 10 61 40 PL-1312 ReO[V] 3-Pyridine propionyl-L-Lys-L-Ala-D-Nal 2-L-Cys-L- 10 71 43 Trp-NH₂ PL-1313 ReO[V] Heptanoyl-L-Ala-L-Trp-D-Arg-L-Cys-L-Phe-NH₂ 1 6 16 PL-1314 ReO[V] C₁₁H₂₃—CO-L-Trp-D-Arg-L-Cys-L-Phe-NH₂ 10 85 53 PL-1315 ReO[V] Ac-L-Arg-L-Trp-L-Nle-L-Cys-L-Phe-NH₂ (SEQ ID 10 70 69 NO: 27) PL-1316 ReO[V] Ac-L-Arg-D-Trp-L-Nle-L-Cys-L-Phe-NH₂ 10 82 91 PL-1317 ReO[V] Ac-L-Trp-L-Nle-D-Phe-L-Cys-L-Arg-NH₂ 10 79 92 PL-1318 ReO[V] C₆H₅—(CH₂)₂—CO-L-Nle-D-Trp-L-Cys-L-Arg-NH₂ 10 82 82 PL-1319 ReO[V] Ac-L-Trp-D-Arg-L-Phe-L-Cys-L-Nle-NH₂ 10 61 89 PL-1320 ReO[V] C₆H₅—(CH₂)₂—CO-L-Arg-L-Trp-L-Cys-L-Nle-NH₂ (SEQ 10 94 96 ID NO: 28) PL-1321 ReO[V] Bz-L-Arg-L-Ala-D-Phe-L-Cys-L-Phe-NH₂ 10 79 93 PL-1322 ReO[V] Bz-L-Arg-L-Ala-D-Trp-L-Cys-L-Phe-NH₂ 10 66 81 PL-1323 ReO[V] Bz-L-Arg-L-Ala-D-Phe-L-Cys-L-Nle-NH₂ 10 77 99 PL-1324 ReO[V] Des-aminoPhe-L-Lys-L-Arg-D-Phe-L-Cys-L-Nle-NH₂ 10 75 93 PL-1325 ReO[V] Des-aminoPhe-L-Cys-D-Phe-L-Arg-L-Phe-NH₂ 10 78 94 PL-1326 ReO[V] Heptanoyl-D-Phe-L-Arg-D-Trp-L-Cys-NH₂ 10 62 68 PL-1327 ReO[V] Heptanoyl-L-Phe-L-Arg-D-Trp-L-Cys-NH₂ 10 87 93 PL-1328 ReO[V] Ac-D-Nal 2-L-Ala-L-Arg-L-Cys-L-Trp-NH₂ 10 78 83 PL-1329 ReO[V] Ac-L-Nle-L-Ala-D-Trp-D-Nal 2-L-Arg-D-Trp-L-Cys- 1 88 30 NH₂ PL-1330 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Nal 2-L-Cys-D-Trp-NH₂ 1 94 53 PL-1331 ReO[V] Des-aminoPhe-L-Cys-D-Phe-L-Arg-L-Nle-NH₂ 10 74 82 PL-1332 ReO[V] Des-aminoPhe-L-Cys-D-Nal 2-L-Arg-Gly-L-Phe-NH₂ 10 98 80 PL-1333 ReO[V] Des-aminoPhe-L-Cys-D-Nal 2-L-Arg-Gly-L-Trp-NH₂ 10 95 77 PL-1334 ReO[V] C₆H₅—(CH₂)₂—CO-L-Nle-L-Trp-L-Cys-L-Arg-NH₂ (SEQ 1 12 26 ID NO: 29) PL-1335 ReO[V] Heptanoyl-L-HPhe-D-Nal 2-L-Arg-L-Trp-L-Cys-NH₂ 1 98 36 PL-1340 ReO[V] D-(N-Bzl)Nal 2-L-Arg-L-Trp-L-Cys-NH₂ 1 99 34 PL-1341 ReO[V] D-(N-PhEt)Nal 2-L-Arg-L-Trp-L-Cys-NH₂ 1 100 46 PL-1342 ReO[V] Ac-L-Nle-L-Arg-D-His-D-Phe-L-Cys-L-Trp-NH₂ 1 37 89 PL-1343 ReO[V] Ac-L-Nle-L-Arg-L-His-D-Phe-L-Cys-L-Trp-NH₂ 10 50 86 PL-1344 ReO[V] Heptanoyl-L-Arg-L-Phe-L-His-L-Cys-L-Trp-NH₂ (SEQ 10 81 89 ID NO: 30) PL-1345 ReO[V] Heptanoyl-L-Arg-L-Phe-D-His-L-Cys-L-Trp-NH₂ 10 80 95 PL-1345 ReO[V] Heptanoyl-L-Arg-L-Phe-D-His-L-Cys-L-Trp-NH₂ 1 52 38 PL-1346 ReO[V] Ph(CH₂)₂—CO-L-His-L-Arg-L-Cys-L-Trp-NH₂ (SEQ ID 10 77 86 NO: 31) PL-1347 ReO[V] Ph(CH₂)₂—CO-D-His-L-Arg-L-Cys-L-Trp-NH₂ 10 70 64 PL-1348 ReO[V] Ac-L-Arg-L-His-L-Phe-L-Cys-L-Trp-NH₂ (SEQ ID 10 51 57 NO: 32) PL-1349 ReO[V] Ac-L-Arg-D-His-L-Phe-L-Cys-L-Trp-NH₂ 10 46 60 PL-1350 ReO[V] Ac-L-Arg-D-His-D-Phe-L-Cys-L-Trp-NH₂ 10 42 70 PL-1351 ReO[V] Ac-L-Arg-L-His-D-Phe-L-Cys-L-Trp-NH₂ 1 6 68 PL-1358 ReO[V] Ac-L-Nle-L-Arg-L-Trp-D-Phe-L-Cys-L-His-NH₂ 10 66 98 PL-1359 ReO[V] Ac-L-Nle-L-Arg-D-Trp-D-Phe-L-Cys-L-His-NH₂ 10 62 90 PL-1360 ReO[V] Ac-L-Arg-L-Trp-L-Phe-L-Cys-L-His-NH₂ (SEQ ID 10 62 57 NO: 33) PL-1362 ReO[V] Ac-L-Arg-L-Trp-D-Phe-L-Cys-L-His-NH₂ 10 59 74 PL-1363 ReO[V] Ac-L-Arg-D-Trp-D-Phe-L-Cys-L-His-NH₂ 10 74 92 PL-1364 ReO[V] Ac-L-Trp-L-Phe-L-His-L-Cys-L-Arg-NH₂ (SEQ ID 10 72 74 NO: 34) PL-1365 ReO[V] Ac-L-Trp-L-Phe-D-His-L-Cys-L-Arg-NH₂ 10 64 71 PL-1366 ReO[V] Ac-L-His-L-Phe-L-Trp-L-Cys-L-Arg-NH₂ (SEQ ID 10 64 78 NO: 35) PL-1367 ReO[V] Ac-L-His-L-Phe-D-Trp-L-Cys-L-Arg-NH₂ 10 73 95 PL-1370 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(4-CF₃)-L-Cys-L-Trp- 1 87 51 NH₂ PL-1371 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(3,4 di-OMe)-L-Cys-L- 1 44 35 Trp-NH₂ PL-1372 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(4-Me)-L-Cys-L-Trp-NH₂ 1 87 82 PL-1373 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(3,4 diCl)-L-Cys-L-Trp- 1 92 54 NH₂ PL-1374 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 89 83 PL-1375 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(3,4 diF)-L-Cys-L-Trp- 1 54 78 NH₂ PL-1376 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Val-L-Cys-L-Trp-NH₂ 1 31 33 PL-1385 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Leu-L-Cys-L-Trp-NH₂ 1 45 34 PL-1386 ReO[V] HOOC—(CH₂)₅—CO-L-His-D-Phe-L-Arg-L-Cys-L-Trp- 0.1 1 71 NH₂ PL-1387 Linear HOOC—(CH₂)₅—CO-L-His-D-Phe-L-Arg-L-Cys-L-Trp- 0.1 1 76 NH₂ PL-1388 ReO[V] NH₂—(CH₂)₅—CO-L-His-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 0.1 −10 80 PL-1389 Linear NH₂—(CH₂)₅—CO-L-His-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 0.1 7 87 PL-1390 ReO[V] L-Lys(Z)-D-His-D-Nal 2-L-Cys-L-Trp-NH₂ 10 63 88 PL-1391 ReO[V] Ac-L-Nle-L-Arg-D-His-D-Nal 2-L-Cys-L-Trp-NH₂ 10 72 103 PL-1391 ReO[V] Ac-L-Nle-L-Arg-D-His-D-Nal 2-L-Cys-L-Trp-NH₂ 1 25 58 PL-1392 ReO[V] B Ala-D-Nle-D-His-D-Nal 2-L-Cys-L-Trp-NH₂ 10 80 84 PL-1393 ReO[V] Bz-L-Arg-D-His-D-Nal 2-L-Cys-L-Trp-NH₂ 10 65 86 PL-1394 ReO[V] Ac-L-His-L-Arg-L-Trp-L-Cys-L-Phe-NH₂ (SEQ ID 10 59 84 NO: 36) PL-1394 ReO[V] Ac-L-His-L-Arg-L-Trp-L-Cys-L-Phe-NH₂ (SEQ ID 1 0 27 NO: 36) PL-1395 ReO[V] Ac-L-His-D-Arg-L-Trp-L-Cys-L-Phe-NH₂ 1 5 10 PL-1395 ReO[V] Ac-L-His-D-Arg-L-Trp-L-Cys-L-Phe-NH₂ 10 78 74 PL-1396 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Nal 2-L-Arg-L-Cys-L-Trp-NH₂ 1 70 96 PL-1405 ReO[V] Heptanoyl-L-Phe-L-His-L-Cys-L-Trp-NH₂ (SEQ ID 1 27 20 NO: 37) PL-1406 ReO[V] Heptanoyl-L-Arg-L-Phe-L-His-L-Cys-L-Trp-NH₂ (SEQ 1 42 32 ID NO: 30) PL-1412 ReO[V] L-Phe-L-His-L-Cys-L-Trp-NH₂ (SEQ ID NO: 38) 1 54 43 PL-1413 ReO[V] Heptanoyl-D-Nal 2-L-Arg-L-Trp-L-Cys-NH₂ 1 86 51 PL-1414 ReO[V] Heptanoyl-Psi D-Nal 2-L-Arg-L-Trp-L-Cys-NH₂ 1 53 26 PL-1415 ReO[V] Heptanoyl-D-Nal 2-Psi-L-Arg-L-Trp-L-Cys-NH₂ 1 0 25 PL-1416 ReO[V] Ac-L-Nle-L-Ala-L-His-L-Phe-L-Arg-L-Cys-L-Trp-NH₂ 1 35 85 (SEQ ID NO: 39) PL-1417 ReO[V] Ac-L-Nle-L-Ala-L-His-L-Phe-D-Arg-L-Cys-L-Trp-NH₂ 1 11 20 PL-1418 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Phe-D-Arg-L-Cys-L-Trp-NH₂ 1 24 80 PL-1419 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Nal 2-L-Arg-L-Cys-L-Trp-NH₂ 1 51 70 PL-1420 ReO[V] Ac-L-Nle-L-Ala-L-His-L-Nal 2-D-Arg-L-Cys-L-Trp-NH₂ 1 52 43 PL-1421 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Nal 2-D-Arg-L-Cys-L-Trp- 1 59 81 NH₂ PL-1422 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(4-Cl)-L-Cys-L-His-NH₂ 1 63 69 PL-1423 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(4-Cl)-L-Cys-L-Phe(4- 1 71 78 NO₂)—NH₂ PL-1424 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(4-Cl)-L-Cys-L-Phe-NH₂ 1 66 85 PL-1425 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(4-Cl)-L-Cys-L-Glu-NH₂ 1 6 39 PL-1426 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(4-Cl)-L-Cys-L-Gln-NH₂ 1 16 71 PL-1427 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 82 90 PL-1428 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-His-L-Cys-L-Trp-NH₂ 1 45 56 PL-1429 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(4-Me)-L-Cys-L-Trp-NH₂ 1 84 80 PL-1430 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-HomoPhe-L-Cys-L-Trp-NH₂ 1 40 26 PL-1431 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phg-L-Cys-L-Trp-NH₂ 1 41 20 PL-1432 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Trp-L-Cys-L-Trp-NH₂ 1 47 38 PL-1433 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Cha-L-Cys-L-Trp-NH₂ 1 38 14 PL-1434 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Chg-L-Cys-L-Trp-NH₂ 1 53 33 PL-1435 ReO[V] Ac-L-Nle-L-Arg-L-His-L-Ala-D-Phe(4-Cl)-L-Cys-L- 1 59 44 Trp-NH₂ PL-1436 ReO[V] Ac-L-Nle-L-His-L-Arg-L-Ala-D-Phe(4-Cl)-L-Cys-L- 1 58 51 Trp-NH₂ PL-1438 ReO[V] Ac-L-Nle-L-Arg-L-His-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 91 89 PL-1439 ReO[V] Ac-L-Nle-L-Arg-D-His-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 43 92 PL-1440 ReO[V] Ac-L-Nle-L-Arg-L-Lys-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 94 79 PL-1441 ReO[V] Ac-L-Nle-L-Arg-D-Lys-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 51 71 PL-1442 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(4-F)-L-Cys-L-Trp-NH₂ 1 85 93 PL-1443 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(4-I)-L-Cys-L-Trp-NH₂ 1 99 72 PL-1444 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Tyr-L-Cys-L-Trp-NH₂ 1 52 68 PL-1445 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(4-NO₂)-L-Cys-L-Trp- 1 83 63 NH₂ PL-1446 ReO[V] L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 1 50 14 PL-1447 ReO[V] Heptanoyl-L-Ala-D-Nal 2-L-Cys-L-Trp-NH₂ 1 44 12 PL-1448 ReO[V] L-Arg-D-Nal 2-L-Cys-L-Trp-NH₂ 1 62 26 PL-1449 ReO[V] Heptanoyl-L-Arg-D-Nal 2-L-Cys-L-Trp-NH₂ 1 80 45 PL-1450 ReO[V] Ac-L-Nle-L-Ala-L-His-L-Phe-L-Arg-L-Cys-L-Trp-NH₂ 1 66 73 (SEQ ID NO: 40) PL-1451 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(4-Br)-L-Cys-L-Trp-NH₂ 1 92 77 PL-1452 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(4-Br)-L-Cys-L-Trp-NH₂ 1 97 86 PL-1457 ReO[V] Ac-L-Ala-L-His-L-Cys-D-Bip-L-Arg-L-Trp-NH₂ 1 79 26 PL-1458 ReO[V] Ac-L-Ala-L-His-L-Cys-D-Phe-L-Arg-L-Trp-NH₂ 1 61 48 PL-1459 ReO[V] Ac-L-Ala-L-His-L-Cys-D-Asp(3Cl-anilino)-L-Arg-L- 1 31 68 Trp-NH₂ PL-1460 ReO[V] Ac-L-Ala-L-His-L-Cys-D-Asp(3,5diCl-anilino)-L-Arg- 1 40 47 L-Trp-NH₂ PL-1461 ReO[V] Ac-L-Ala-L-His-L-Cys-D-Asp(anilino)-L-Arg-L-Trp- 1 60 43 NH₂ PL-1462 ReO[V] Heptanoyl-L-His-D-Phe-L-Arg-L-Cys-L-Nal 2-NH₂ 1 39 99 PL-1463 ReO[V] Heptanoyl-L-His-D-Phe-L-Arg-D-Cys-L-Nal 2-NH₂ 1 57 93 PL-1464 ReO[V] Heptanoyl-L-His-D-Phe-L-Arg-L-Cys-D-Nal 2-NH₂ 1 80 94 PL-1465 ReO[V] Heptanoyl-L-His-D-Phe-L-Arg-D-Cys-D-Nal 2-NH₂ 1 48 84 PL-1466 ReO[V] Heptanoyl-L-His-D-Phe-D-Arg-L-Cys-L-Trp-NH₂ 1 37 67 PL-1467 ReO[V] Heptanoyl-L-His-D-Phe-D-Arg-D-Cys-L-Trp-NH₂ 1 47 69 PL-1478 ReO[V] Ac-L-Arg-L-Phe-L-Phe-L-Cys-L-Ser-NH₂ (SEQ ID 1 21 28 NO: 41) PL-1480 ReO[V] Ac-L-Arg-D-Phe-L-Phe-L-Cys-L-Ser-NH₂ 1 9 21 PL-1481 ReO[V] Ac-L-Arg-D-Phg-L-Phe-L-Cys-L-Ser-NH₂ 1 15 19 PL-1483 ReO[V] Ac-L-Arg-L-Phe-L-Nal 2-L-Cys-L-Ser-NH₂ 1 31 56 PL-1484 ReO[V] Ac-L-Arg-D-Phe-L-Nal 2-L-Cys-L-Ser-NH₂ 1 37 72 PL-1485 ReO[V] Ac-L-Arg-D-Phg-L-Nal 2-L-Cys-L-Ser-NH₂ 1 41 60 PL-1486 ReO[V] Ac-D-Ala-L-His-L-Cys-D-Nal 2-L-Arg-L-Trp-NH₂ 1 90 26 PL-1488 Linear Ac-D-Ala-L-His-L-Cys-D-Nal 2-L-Arg-L-Trp-NH₂ 1 85 35 PL-1489 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Nal 2-L-Arg-L-Trp-L-Cys- 1 99 30 NH₂ PL-1490 Linear Heptanoyl-L-Ser(Bzl)-D-Nal 2-L-Arg-L-Trp-L-Cys- 1 86 48 NH₂ PL-1491 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Nal 2-L-Arg-L-Phe-L-Cys- 1 76 66 NH₂ PL-1492 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Nal 2-L-Arg-D-Phe-L-Cys- 1 90 63 NH₂ PL-1493 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Nal 2-L-Arg-D-Trp-L-Cys- 1 102 26 NH₂ PL-1494 ReO[V] Ac-L-Lys-L-Cys-D-Phe-L-Trp-L-Nle-NH₂ 1 30 27 PL-1496 ReO[V] Ac-L-Asp-L-Lys-L-Pro-L-Pro-L-Arg-L-Ala-D-Nal 2-L- 1 59 43 Cys-L-Trp-NH₂ PL-1497 ReO[V] L-Asp-L-Lys-L-Pro-L-Pro-L-Arg-L-Ala-D-Nal 2-L-Cys- 1 71 47 L-Trp-NH₂ PL-1498 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Nal 2-L-Cys-L-Trp-Ahx-L- 1 86 59 Lys-L-Asp-NH₂ PL-1499 ReO[V] Heptanoyl-L-Lys-D-Phe-L-Trp-L-Cys-NH₂ 1 20 23 PL-1500 ReO[V] Heptanoyl-D-Phe-L-Trp-L-Cys-L-Lys-NH₂ 1 33 25 PL-1501 ReO[V] Heptanoyl-L-His-D-Trp-L-Cys-L-Trp-NH₂ 1 44 78 PL-1502 ReO[V] Heptanoyl-L-His-D-Trp-Gly-L-Cys-L-Lys-NH₂ 1 41 29 PL-1503 ReO[V] Heptanoyl-L-Phe-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 1 41 52 PL-1504 ReO[V] Ac-L-Arg-L-Phe-L-Nal 2-L-Asn-L-Cys-L-Phe-NH₂ 1 21 36 (SEQ ID NO: 42) PL-1505 ReO[V] Ac-L-Arg-L-Phe-L-Nal 2-L-Asn-L-Cys-L-Phe-NH₂ 1 29 45 (SEQ ID NO: 42) PL-1506 ReO[V] Ac-L-Arg-D-Phe-L-Nal 2-L-Asn-L-Cys-L-Phe-NH₂ 1 22 30 PL-1507 ReO[V] Ac-L-Arg-L-Phe-L-Phe-L-Asn-L-Cys-L-Phe-NH₂ 1 22 20 (SEQ ID NO: 43) PL-1508 ReO[V] Ac-L-Arg-D-Phe-L-Phe-L-Asn-L-Cys-L-Phe-NH₂ 1 31 20 PL-1509 ReO[V] Ac-L-Arg-L-Phe-L-Cys-L-Phe-L-Asn-L-Ala-L-Phe- 1 30 19 NH₂ (SEQ ID NO: 44) PL-1510 ReO[V] Ac-L-Arg-L-Phe-L-Phe-L-Cys-L-Asn-L-Ala-L-Phe- 1 31 21 NH₂ (SEQ ID NO: 45) PL-1511 ReO[V] Ac-L-Arg-L-Phe-L-Phe-L-Asn-L-Cys-L-Ala-L-Phe- 1 26 21 NH₂ (SEQ ID NO: 46) PL-1512 ReO[V] Ac-L-Arg-L-Phe-L-Phe-L-Asn-L-Ala-L-Cys-L-Phe- 1 24 20 NH₂ (SEQ ID NO: 47) PL-1513 ReO[V] Ac-L-Arg-L-Phe-L-Phe-L-Asn-L-Phe-L-Cys-NH₂ 1 18 23 (SEQ ID NO: 48) PL-1514 ReO[V] Ac-L-Arg-L-Phe-L-Phe-L-Asn-L-Phe-L-Cys-NH₂ 1 30 28 (SEQ ID NO: 48) PL-1515 ReO[V] Heptanoyl-L-His-D-Phe-L-Lys-L-Cys-L-Glu 1 34 21 PL-1518 ReO[V] Heptanoyl-L-Cys-D-Phe-L-Trp-L-Lys-NH₂ 1 25 8 PL-1519 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Nal 2-L-Cys-L-Trp-L-Pro-L- 1 60 22 Pro-L-Lys-L-Asp-NH₂ PL-1522 ReO[V] Ac-L-Nle-L-Arg-L-His-D-Phe(4-Br)-L-Cys-L-Trp-NH₂ 1 91 87 PL-1523 ReO[V] Ac-L-Nle-L-Arg-L-Ala-L-His-D-Phe(4-Br)-L-Cys-L- 1 59 69 Trp-NH₂ PL-1524 ReO[V] Ac-L-Nle-L-Arg-L-His-L-Ala-D-Phe(4-Br)-L-Cys-L- 1 44 36 Trp-NH₂ PL-1525 ReO[V] Ac-L-Nle-L-Arg-L-Phe(4-Br)-L-Ala-L-His-L-Cys-L- 1 41 57 Trp-NH₂ PL-1526 ReO[V] Ac-L-Nle-L-Arg-L-Trp-L-Ala-D-Phe(4-Br)-L-Cys-L- 1 34 63 His-NH₂ PL-1581 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Phe-L-Arg-L-Trp-L-Cys-NH₂ 1 98 91 PL-1582 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Phe-L-Cys-L-Arg-L-Trp-NH₂ 1 66 93 PL-1583 ReO[V] Ac-L-Nle-L-Ala-L-His-L-Cys-D-Phe-L-Arg-L-Trp-NH₂ 1 75 84 PL-1584 ReO[V] Ac-L-Nle-L-His-L-Cys-L-His-D-Phe-L-Arg-L-Trp-NH₂ 1 71 96 PL-1585 ReO[V] Ac-L-Nle-L-Ala-L-His-L-Phe-L-Cys-L-Arg-L-Trp-NH₂ 1 22 45 PL-1587 ReO[V] Ac-L-Nle-L-Arg-L-Arg-D-Nal 2-L-Cys-L-Trp-NH₂ 1 98 96 PL-1592 ReO[V] Ac-L-Nle-L-Ala-L-Arg-L-His-D-Phe-L-Cys-L-Trp-NH₂ 1 7 19 PL-1593 ReO[V] Ac-L-Nle-L-Ala-D-Arg-L-His-D-Phe-L-Cys-L-Trp-NH₂ 1 16 71 PL-1594 ReO[V] Ac-L-Nle-L-Ala-L-His-D/L-Atc-L-Arg-L-Cys-L-Trp-NH₂ 1 24 100 PL-1595 ReO[V] Ac-L-Nle-L-Ala-L-His-Aic-L-Arg-L-Cys-L-Trp-NH₂ 1 3 60 (SEQ ID NO: 49) PL-1597 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D/L-Atc-L-Cys-L-Trp-NH₂ 1 11 68 PL-1598 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Qal(2′)-L-Cys-L-Trp-NH₂ 1 9 22 PL-1605 ReO[V] Ac-L-Nle-L-Arg-L-Arg-D-2-L-Cys-L-Trp-NH₂ 1 100 100 PL-1606 ReO[V] Ac-L-Nle-L-Arg-L-Ala-Aic-L-Cys-L-Trp-NH₂ (SEQ ID 1 63 44 NO: 50) PL-1607 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Qal(2′)-L-Arg-L-Cys-L-Trp- 1 52 100 NH₂ PL-1621 ReO[V] Ac-L-Nle-L-Ala-L-His-Achc-L-Arg-L-Cys-L-Trp-NH₂ 1 34 36 (SEQ ID NO: 51) PL-1623 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Sal-L-Arg-L-Cys-L-Trp-NH₂ 1 55 92 PL-1624 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Sal-L-Cys-L-Trp-NH₂ 1 48 25 PL-1626 ReO[V] Ac-L-Nle-L-Arg-L-Trp-D-Nal 2-L-Cys-L-Trp-NH₂ 1 54 66 PL-1633 ReO[V] Ac-L-Nle-D-Arg-L-Arg-D-Nal 2-L-Cys-L-Trp-NH₂ 1 87 86 PL-1633 ReO[V] Ac-L-Nle-D-Arg-L-Arg-D-Nal 2-L-Cys-L-Trp-NH₂ 1 87 91 PL-1634 ReO[V] Ac-L-Nle-L-Arg-D-Arg-D-Nal 2-L-Cys-L-Trp-NH₂ 1 50 42 PL-1635 ReO[V] Ac-L-Nle-L-Arg-L-Ala-Acpc-L-Cys-L-Trp-NH₂ (SEQ 1 43 14 ID NO: 52) PL-1636 ReO[V] Ac-L-Nle-L-Ala-L-His-Acpc-L-Arg-L-Cys-L-Trp-NH₂ 1 38 20 (SEQ ID NO: 53) PL-1638 ReO[V] Ac-L-Nle-L-Arg-L-Arg-D-Qal(2′)-L-Cys-L-Trp-NH₂ 1 48 67 PL-1649 ReO[V] Ac-L-His-Gly-Gly-L-Cys-L-Trp-NH₂ (SEQ ID NO: 54) 10 62 19 PL-1650 ReO[V] Ac-L-His-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 10 66 52 PL-1651 ReO[V] Ac-L-His-D-Phe-D-Arg-L-Cys-L-Trp-NH₂ 10 58 95 PL-1652 ReO[V] Ac-L-His-L-Phe-D-Arg-L-Cys-L-Trp-NH₂ 10 40 11 PL-1655 ReO[V] Ac-L-His-L-Phe-L-Arg-L-Cys-L-Trp-NH₂ (SEQ ID 10 51 45 NO: 8) PL-1658 ReO[V] Ac-L-Nle-L-Arg-L-Arg-D-Phe(3,4-diCl)-L-Cys-L-Trp- 1 100 99 NH₂ PL-1658 ReO[V] Ac-L-Nle-L-Arg-L-Arg-D-Phe(3,4-diCl)-L-Cys-L-Trp- 1 97 93 NH₂ PL-1659 ReO[V] Ac-L-Nle-L-Lys-L-Lys-D-L-Cys-L-Trp-NH₂ 1 91 58 PL-1660 ReO[V] Ac-L-Nle-L-Arg-L-Arg-D-Phe-L-Cys-L-Trp-NH₂ 1 67 100 PL-1661 ReO[V] Ac-L-Nle-L-Cit-L-Cit-D-Nal 2-L-Cys-L-Trp-NH₂ 1 58 27 PL-1662 ReO[V] Ac-L-Nle-L-Ala-L-Arg-L-Arg-D-Nal 2-L-Cys-L-Trp- 1 93 69 NH₂ PL-1663 ReO[V] Ac-L-Nle-L-Arg-L-Arg-D-Trp-L-Cys-L-Trp-NH₂ 1 85 81 PL-1664 ReO[V] Ac-L-Nle-L-Arg-L-Arg-D-Nal 2-L-Cys-NH₂ 1 100 96 PL-1665 ReO[V] Ac-L-Arg-L-Arg-D-Nal 2-L-Cys-L-Trp-NH₂ 1 93 94 PL-1666 ReO[V] Ac-L-Nle-L-Arg-L-Arg-D-Phe(p-I)-L-Cys-L-Trp-NH₂ 1 101 101 PL-1667 ReO[V] Heptanoyl-L-Arg-L-Arg-D-Nal 2-L-Cys-L-Trp-NH₂ 1 97 92 PL-1684 ReO[V] Ac-L-Val-L-Pro-L-Arg-L-Ala-D-Nal 2-L-Cys-L-Trp- 1 36 26 NH₂ PL-1685 ReO[V] Ac-L-Nle-L-Arg-BAla-D-Nal 2-L-Cys-L-Trp-NH₂ 1 83 54 PL-1686 ReO[V] Ac-L-Nle-D-Arg-D-Arg-L-Nal 2-L-Cys-L-Trp-NH₂ 1 24 23 PL-1690 ReO[V] Ac-L-Nle-D-Arg-L-Arg-D-Nal 2-L-Cys-L-Trp-NH₂ 1 94 71 PL-1691 Linear Heptanoyl-L-His-D-Phe-L-Arg-L-Cys-L-Trp-L-Lys- 1 90 62 NH₂ PL-1692 Linear NH₂—(CH₂)₅—CO-L-His-D-Phe-L-Arg-L-Cys-L-Trp-L- 1 79 60 Lys-NH₂ PL-1694 ReO[V] Heptanoyl-L-His-D-Phe-L-Arg-L-Cys-L-Trp-L-Lys- 1 43 61 NH₂ PL-1695 ReO[V] NH₂—(CH₂)₅—CO-L-His-D-Phe-L-Arg-L-Cys-L-Trp-L- 1 44 87 Lys-NH₂ PL-1702 ReO[V] Ac-L-His-L-Arg-L-Arg-D-Nal 2-L-Cys-NH₂ 1 83 62 PL-1703 ReO[V] Ac-L-Trp-L-Arg-L-Arg-D-Nal 2-L-Cys-NH₂ 1 95 73 PL-1704 ReO[V] Ac-L-Phe-L-Arg-L-Arg-D-Nal 2-L-Cys-NH₂ 1 98 75 PL-1705 ReO[V] Ac-L-Lys-L-Arg-L-Arg-D-Nal 2-L-Cys-NH₂ 1 90 53 PL-1706 ReO[V] Ac-L-Ser-L-Arg-L-Arg-D-Nal 2-L-Cys-NH₂ 1 89 60 PL-1707 ReO[V] Ac-L-Glu-L-Arg-L-Arg-D-Nal 2-L-Cys-NH₂ 1 46 36 PL-1708 ReO[V] Ac-L-Arg-L-His-L-Cys-D-Nal 2-L-Arg-L-Trp-NH₂ 1 99 34 PL-1709 ReO[V] Ac-D-Ala-L-His-L-Cys-L-Arg-D-Nal 2-L-Arg-L-Trp- 1 100 98 NH₂ PL-1710 ReO[V] Ac-D-Ala-L-Arg-L-Cys-D-Nal 2-L-Arg-L-Trp-NH₂ 1 99 25 PL-1718 ReO[V] Ac-L-Nle-L-Arg-L-Ala-D-Phe(3-Cl)-L-Cys-L-Trp-NH₂ 1 59 35 PL-1722 ReO[V] Ac-L-Trp-L-Arg-L-Arg-D-Phe-L-Cys-NH₂ 1 29 38 PL-1723 ReO[V] Ac-L-Nle-L-Arg-L-Arg-D-Nal 2-L-Cys-OH 1 85 66 PL-1726 ReO[V] Ac-L-Nle-L-Arg-L-Hphe-D-Phe(4-Cl)-L-Cys-NH₂ 1 70 42 PL-1727 ReO[V] Ac-L-Nle-L-Arg-L-Pal 2′-D-Phe(4-Cl)-L-Cys-NH₂ 1 84 62 PL-1728 ReO[V] Ac-L-Nle-L-Arg-L-Phe-D-Phe(4-Cl)-L-Cys-NH₂ 1 73 53 PL-1730 ReO[V] Ac-L-Nle-L-Arg-L-Nal 1-D-Phe(4-Cl)-L-Cys-NH₂ 1 35 39 PL-1731 ReO[V] Ac-L-Nle-L-Arg-L-Nal 2-D-Phe(4-Cl)-L-Cys-NH₂ 1 63 38 PL-1732 ReO[V] Ac-L-Nle-L-Arg-L-Trp-D-Phe(4-Cl)-L-Cys-NH₂ 1 74 53 PL-1733 ReO[V] L-Tic-D-Phe(4-Cl)-L-Cys-NH₂ 1 8 14 PL-1734 ReO[V] L-Tic-D-Phe(4-Cl)-L-Trp-L-Cys-NH₂ 1 7 6 PL-1735 ReO[V] L-Tic-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 13 12 PL-1736 ReO[V] Ac-D-Ala-L-His-L-Cys-D-(N-Bzl)Phe-L-Arg-L-Trp-NH₂ 1 3 6 PL-1737 ReO[V] Ac-D-Ala-L-His-L-Cys-L-(N-Bzl)Phe-L-Arg-L-Trp-NH₂ 1 3 48 PL-1738 ReO[V] Ac-D-Ala-L-His-L-Cys-D-(N-Bzl)Nal 2-L-Arg-L-Trp- 1 23 13 NH₂ PL-1751 ReO[V] Ac-L-His-L-(N-2′naphthalene)Phe-L-Arg-L-Trp-L- 1 70 78 Cys-NH₂ (SEQ ID NO: 55) PL-1752 ReO[V] Ac-D-Ala-L-His-L-Cys-L-(N-2′naphthalene)Phe-L- 1 5 29 Arg-L-Trp-NH₂ PL-1753 ReO[V] Ac-D-Ala-L-His-L-Cys-D-(N-2′naphthalene)Phe-L- 1 22 50 Arg-L-Trp-NH₂ PL-1754 ReO[V] D-Tic-D-Phe(4-Cl)-L-Trp-L-Cys-NH₂ 1 7 4 PL-1755 ReO[V] Ac-L-Arg-L-Lys-L-Phe-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 40 48 PL-1756 ReO[V] Ac-L-Nle-L-Lys-L-Phe-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 63 64 PL-1757 ReO[V] Ac-L-Arg-L-Lys-L-Leu-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 45 38 PL-1758 ReO[V] Ac-L-Nle-L-Lys-L-Leu-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 94 78 PL-1759 ReO[V] Ac-L-Arg-L-Phe-L-Lys-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 62 61 PL-1760 ReO[V] Ac-L-Nle-L-Phe-L-Lys-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 72 84 PL-1761 ReO[V] Ac-L-Arg-L-Leu-L-Lys-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 16 51 PL-1762 ReO[V] Ac-L-Nle-L-Leu-L-Lys-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 69 82 PL-1774 ReO[V] Ac-L-Nle-L-Lys-L-Val-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 83 79 PL-1775 ReO[V] Ac-L-Nle-L-Lys-L-Ile-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 78 57 PL-1776 ReO[V] Ac-L-Nle-L-Lys-L-Nle-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 76 33 PL-1777 ReO[V] Ac-L-Nle-L-Lys-L-Thr-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 79 86 PL-1778 ReO[V] Ac-L-Nle-L-Lys-L-Tle-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 89 60 PL-1779 ReO[V] Ac-L-Nle-L-Lys-L-Chg-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 85 71 PL-1780 ReO[V] Ac-L-Nle-L-Lys-L-Cha-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 77 34 PL-1781 ReO[V] Ac-L-Nle-L-Lys-L-Trp-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 69 66 PL-1782 ReO[V] Ac-L-Nle-L-Lys-L-Hphe-D-Phe(4-Cl)-L-Cys-L-Trp- 1 67 14 NH₂ PL-1783 ReO[V] Ac-L-Nle-L-Lys-L-Lys(Z)-D-Phe(4-Cl)-L-Cys-L-Trp- 1 72 87 NH₂ PL-1785 ReO[V] Ac-D-Ala-L-His-L-Cys-D-Tic-L-Arg-L-Trp-NH₂ 1 16 51 PL-1787 ReO[V] Ac-D-Ala-L-His-L-Cys-D-3,3,Dip-L-Arg-L-Trp-NH₂ 1 31 49 PL-1788 ReO[V] Ac-L-Ala-L-His-D-Phe-L-Arg-L-Trp-L-Cys-NH₂ 1 78 62 PL-1789 ReO[V] Ac-L-Pro-L-Ala-L-His-D-Phe-L-Arg-L-Trp-L-Cys-NH₂ 1 87 63 PL-1790 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Phe-L-Arg-L-Trp-L-Cys-L- 1 99 93 Trp-NH₂ PL-1791 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Phe-L-Arg-L-Trp-L-Cys-L- 1 98 87 Leu-NH₂ PL-1792 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Phe-L-Arg-L-Trp-L-Cys-L- 1 100 96 Lys-NH₂ PL-1793 ReO[V] Ac-L-Pro-L-His-D-Phe-L-Arg-D-Trp-L-Cys-NH₂ 1 39 41 PL-1794 ReO[V] Ac-L-Pro-L-His-D-Phe-L-Arg-D-Trp-L-Cys-D-Trp-NH₂ 1 20 −7 PL-1795 ReO[V] Ac-D-Tic-D-Phe-L-Arg-D-Trp-L-Cys-NH₂ 1 85 51 PL-1796 ReO[V] Ac-D(3,3)Bpa-D-Phe-L-Arg-D-Trp-L-Cys-NH₂ 1 14 −7 PL-1797 ReO[V] Ac-L-Lys-L-Leu-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 42 49 PL-1798 ReO[V] Heptanoyl-L-Lys-L-Leu-D-Phe(4-Cl)-L-Cys-L-Trp- 1 56 68 NH₂ PL-1799 ReO[V] Ac-L-Nle-L-Lys-L-Leu-D-Phe(4-Cl)-L-Cys-NH₂ 1 69 70 PL-1800 ReO[V] Ac-L-Nle-L-Lys-L-Leu-D-Phe(4-Cl)-D-Cys-L-Trp-NH₂ 1 35 54 PL-1801 ReO[V] Ac-L-Nle-L-Lys-L-Leu-D-Phe(4-Cl)-L-Cys-L-Tic-NH₂ 1 64 89 PL-1802 ReO[V] Ac-L-Nle-L-Lys-L-Leu-D-Phe(4-Cl)-L-Cys-L-Tyr-NH₂ 1 16 72 PL-1803 ReO[V] Ac-L-Nle-L-Lys-L-Leu-D-Phe(4-Cl)-L-Cys-L-Leu-NH₂ 1 23 55 PL-1804 ReO[V] Ac-L-Nle-L-Lys-L-Leu-D-Phe(4-Cl)-L-Cys-L-Tyr(Bzl)- 1 47 70 NH₂ PL-1805 ReO[V] Ac-L-Nle-L-Lys-L-Leu-D-Phe(4-Cl)-L-Cys-L-Phe(3- 1 67 74 Cl)—NH2 PL-1806 ReO[V] Ac-L-Nle-L-Ala-L-His-L-Phe-L-Arg-L-Cys-L-Trp-NH₂ 1 13.0 66.0 PL-1807 ReO[V] Ac-L-Nle-L-Glu-L-His-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 1 38.0 96.0 PL-1808 ReO[V] Ac-L-His-D-Phe-L-Arg-L-Trp-L-Cys-L-Lys-L-Pro-L- 1 75.0 94.0 Val-NH₂ PL-1809 ReO[V] L-Tyr-L-Val-L-Nle-Gly-L-His-L-Phe-L-Arg-L-Trp-L- 1 77.0 88.0 Asp-L-Arg-L-Cys-L-Phe-NH₂ (SEQ ID NO: 56) PL-1810 ReO[V] L-Tyr-L-Val-L-Nle-Gly-L-His-L-Phe-L-Arg-L-Trp-L- 1 88.0 91.0 Asp-L-Cys-L-Arg-L-Phe-NH₂ (SEQ ID NO: 57) PL-1811 ReO[V] L-Tyr-L-Val-L-Nle-Gly-L-His-L-Phe-L-Arg-L-Trp-L- 1 92.0 95.0 Cys-L-Asp-L-Arg-L-Phe-NH₂ (SEQ ID NO: 58) PL-1812 ReO[V] L-Tyr-L-Val-L-Nle-Gly-L-His-L-Phe-L-Arg-L-Cys-L- 1 98.0 98.0 Trp-L-Asp-L-Arg-L-Phe-NH₂ (SEQ ID NO: 59) PL-1813 ReO[V] L-Tyr-L-Val-L-Nle-Gly-L-His-L-Phe-L-Cys-L-Arg-L- 1 36.0 67.0 Trp-L-Asp-L-Arg-L-Phe-NH₂ (SEQ ID NO: 60) PL-1814 ReO[V] L-Tyr-L-Val-L-Nle-Gly-L-His-L-Cys-L-Phe-L-Arg-L- 1 26.0 62.0 Trp-L-Asp-L-Arg-L-Phe-NH₂ (SEQ ID NO: 61) PL-1815 ReO[V] L-Tyr-L-Val-L-Nle-Gly-L-Cys-L-His-Phe-L-Arg-L-Trp- 1 36.0 60.0 L-Asp-L-Arg-L-Phe-NH₂ (SEQ ID NO: 62) PL-1816 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(2-Cl)-L-Arg-D-Trp-L- 1 83.0 46.0 Cys-NH₂ PL-1817 ReO[V] Bz-L-His-Gly-D-Phe(2-Cl)-L-Arg-D-Trp-L-Cys-NH₂ 1 68.0 45.0 PL-1818 ReO[V] Ac-L-Nle-L-Ala-D-Trp-D-Phe(2-Cl)-L-Arg-D-Trp-L- 1 36.0 15.0 Cys-NH₂ PL-1819 ReO[V] Ac-L-Ala-L-His-D-Phe(2-Cl)-L-Arg-D-Trp-L-Cys-NH₂ 1 67.0 76.0 PL-1820 ReO[V] Bz-D-Phe(2-Cl)-L-Arg-D-Trp-L-Cys-NH₂ 1 54.0 17.0 PL-1821 ReO[V] Lys(Z)-L-Ala-D-Phe-L-Cys-L-Trp-NH₂ 1 18 43 PL-1822 ReO[V] Lys(Z)-L-Ala-D-Phe(2-Cl)-L-Cys-L-Trp-NH₂ 1 15 24 PL-1823 ReO[V] Lys(Z)-L-Ala-D-Phe(3-Cl)-L-Cys-L-Trp-NH₂ 1 35 11 PL-1824 ReO[V] Lys(Z)-L-Ala-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 69 34 PL-1825 ReO[V] Lys(Z)-L-Ala-D-Phe-(3,4-diCl)-L-Cys-L-Trp-NH₂ 1 58 15 PL-1828 ReO[V] Heptanoyl-L-Tyr-D-Phe(2-Cl)-L-Arg-D-Trp-L-Cys- 1 29 29 NH₂ PL-1829 ReO[V] Heptanoyl-L-Trp-D-Phe(2-Cl)-L-Arg-D-Trp-L-Cys- 1 18 10 NH₂ PL-1830 ReO[V] Heptanoyl-L-Nal 2-D-Phe(2-Cl)-L-Arg-D-Trp-L-Cys- 1 5 11 NH₂ PL-1831 ReO[V] Heptanoyl-L-Bip-D-Phe(2-Cl)-L-Arg-D-Trp-L-Cys- 1 −2 13 NH₂ PL-1832 ReO[V] Heptanoyl-L-Phe(3,4-diCl)-D-Phe(2-Cl)-L-Arg-D-Trp- 1 25 12 L-Cys-NH₂ PL-1833 ReO[V] Heptanoyl-L-Tle-D-Phe(2-Cl)-L-Arg-D-Trp-L-Cys-NH₂ 1 59 49 PL-1834 ReO[V] Heptanoyl-L-Cha-D-Phe(2-Cl)-L-Arg-D-Trp-L-Cys- 1 16 46 NH₂ PL-1835 ReO[V] Heptanoyl-L-Phe(p-NO₂)-D-Phe(2-Cl)-L-Arg-D-Trp-L- 1 20 15 Cys-NH₂ PL-1836 ReO[V] Heptanoyl-L-HPhe-D-Phe(2-Cl)-L-Arg-D-Trp-L-Cys- 1 82 50 NH₂ PL-1837 ReO[V] Heptanoyl-L-Tic-D-Phe(2-Cl)-L-Arg-D-Trp-L-Cys-NH₂ 1 42 24 PL-1838 ReO[V] D-Tic-L-Arg-L-Trp-L-Cys-NH₂ 1 54 74 PL-1839 ReO[V] Ac-D-Tic-D-Phe-L-Arg-L-Trp-L-Cys-NH₂ 1 11 35 PL-1840 ReO[V] Ac-L-Tic-D-Phe-L-Arg-L-Trp-L-Cys-NH₂ 1 34 24 PL-1841 ReO[V] Ac-L-Pro-L-His-D-Phe-L-Arg-L-Trp-L-Cys-NH₂ 1 34 61 PL-1842 ReO[V] Ac-L-Nle-L-Ala-L-His-L-Arg-L-Phe-L-Trp-L-Cys-NH₂ 1 2 27 (SEQ ID NO: 63) PL-1843 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Arg-L-Phe-L-Trp-L-Cys-NH₂ 1 −8 16 PL-1844 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Phe-L-Arg-L-Trp-D-Cys-L- 1 83 98 Trp-NH₂ PL-1845 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Phe-L-Arg-L-Trp-L-Cys-D- 1 96 99 Trp-NH₂ PL-1846 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Phe-L-Arg-L-Cys-L-Trp-NH₂ 0.1 4 85 PL-1849 ReO[V] C₆H₅—CO-L-Lys-D-Phe-L-Cys-L-Trp-NH₂ 1 12 39 PL-1850 ReO[V] C₆H₅—CH═CH—CO-L-Lys-D-Phe-L-Cys-L-Trp-NH₂ 1 −2 24 PL-1851 ReO[V] Pyridine-3-CO-L-Lys-D-Phe-L-Cys-L-Trp-NH₂ 1 −5 26 PL-1852 ReO[V] Tetralin-2-CO-L-Lys-D-Phe-L-Cys-L-Trp-NH₂ 1 0 15 PL-1853 ReO[V] Naphthalene-1-CO-L-Lys-D-Phe-L-Cys-L-Trp-NH₂ 1 9 27 PL-1854 ReO[V] Naphthalene-2-CO-L-Lys-D-Phe-L-Cys-L-Trp-NH₂ 1 −6 24 PL-1855 ReO[V] Lys(Z)-Gly-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 0 32 PL-1856 ReO[V] Lys(Z)-L-Val-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 31 53 PL-1857 ReO[V] Lys(Z)-L-Nle-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 32 40 PL-1858 ReO[V] Lys(Z)-L-Leu-D-Phe(4-Cl)-L-Cys-L-Trp-NH₂ 1 31 36 PL-1859 ReO[V] Ac-L-Phe-L-Phe-L-Cys-L-Tic-L-Lys-NH₂ (SEQ ID 1 −8 9 NO: 64) PL-1860 ReO[V] Ac-L-Phe-L-Phe-L-Cys-L-Inp-L-Lys-NH₂ (SEQ ID 1 0 6 NO: 65) PL-1861 ReO[V] Ac-L-Phe-L-Phe-L-Cys-4-Abz-L-Lys-NH₂ (SEQ ID 1 −14 0 NO: 66) PL-1862 ReO[V] Ac-L-Phe-L-Phe-L-Cys-3-Abz-L-Lys-NH₂ (SEQ ID 1 −7 17 NO: 67) PL-1863 ReO[V] Ac-L-Phe-L-Phe-L-Cys-2-Abz-L-Lys-NH₂ (SEQ ID 1 6 19 NO: 68) PL-1864 ReO[V] Ac-L-Phe-D-Trp-L-Cys-2-Abz-L-Lys-NH₂ 1 −7 17 PL-1865 ReO[V] Ac-L-Ser(Bzl)-D-Phe(2-Cl)-L-Arg-D-Trp-L-Cys-NH₂ 1 40 13 PL-1866 ReO[V] Bz-L-Ser(Bzl)-D-Phe(2-Cl)-L-Arg-D-Trp-L-Cys-NH₂ 1 30 16 PL-1867 ReO[V] Heptanoyl-L-Asn-D-Phe(2-Cl)-L-Arg-D-Trp-L-Cys- 1 60 52 NH₂ PL-1868 ReO[V] Heptanoyl-L-Asp-D-Phe(2-Cl)-L-Arg-D-Trp-L-Cys- 1 −3 5 NH₂ PL-1869 ReO[V] Heptanoyl-L-Lys(NH-Bz)-D-Phe(2-Cl)-L-Arg-D-Trp-L- 1 42 25 Cys-NH₂ PL-1870 ReO[V] Heptanoyl-D-B-Hphe(4-F)-L-Arg-D-Trp-L-Cys-NH₂ 1 11 12 PL-1871 ReO[V] Heptanoyl-D-B-Hphe(2-Cl)-L-Arg-D-Trp-L-Cys-NH₂ 1 3 10 PL-1872 ReO[V] Ac-D-Ala-L-His-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 79 27 PL-1873 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Phe-L-Arg-D-Cys-Trp-NH₂ 1 31 92.6 PL-1874 ReO[V] Ac-L-Nle-L-Ala-L-His-D-Phe-L-Arg-L-Trp-D-Cys-D- 1 90 98 Trp-NH₂ PL-1875 ReO[V] 1-Naphthalene-acetyl-L-Lys-L-Ala-D-Phe(4-Cl)-L- 1 77 34 Cys-Trp-NH₂ PL-1876 ReO[V] 2-Naphthalene-acetyl-L-Lys-L-Ala-D-Phe(4-Cl)-L- 1 52 8 Cys-Trp-NH₂ PL-1877 ReO[V] 3-Bromophenyl acetyl-L-Lys-L-Ala-D-Phe(4-I)-L-Cys- 1 92 31 Trp-NH₂ PL-1878 ReO[V] 4-Bromophenyl acetyl-L-Lys-L-Ala-D-Phe(p-I)-L-Cys- 1 75 53 Trp-NH₂ PL-1879 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(3-Cl)-L-Arg-D-Trp-L- 1 86 28 Cys-NH₂ PL-1880 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(3,4-Cl₂)-L-Arg-D-Trp-L- 1 96 18 Cys-NH₂ PL-1881 ReO[V] Heptanoyl-L-Ser(Bzl)-D-HPhe-L-Arg-D-Trp-L-Cys- 1 −6 16 NH₂ PL-1882 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Tic-L-Arg-D-Trp-L-Cys-NH₂ 1 −14 11 PL-1883 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(4-Cl)-L-Arg-D-Trp-L- 1 97 49 Cys-NH₂ PL-1884 ReO[V] Ac-D-Phe-L-His-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 64 32 PL-1885 ReO[V] Ac-D-Nle-L-His-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 84 68 PL-1886 ReO[V] Ac-D-HPhe-L-His-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp- 1 73 62 NH₂ PL-1887 ReO[V] Ac-D-Phe-L-Phe-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp- 1 50 24 NH₂ PL-1888 ReO[V] Ac-D-Ala-L-Nle-L-Cys-D-Phe(2-Cl)$$-L-Arg-L-Trp-NH₂ 1 90 40 PL-1889 ReO[V] Ac-L-Nle-L-His-L-Cys-D-Phe(2-Cl)$$-L-Arg-L-Trp-NH₂ 1 49 58 PL-1890 ReO[V] Heptanoyl-D-Ala-L-His-L-Cys-D-Phe(2-Cl)-L-Arg-L- 1 24 31 Trp-NH₂ PL-1891 ReO[V] Heptanoyl-L-Ser(Bzl)-D-BHphe(2-Cl)-L-Arg-D-Trp-L- 1 −7 10 Cys-NH₂ PL-1892 ReO[V] Heptanoyl-L-Ser(Bzl)-D-BHphe(2-F)-L-Arg-D-Trp-L- 1 6 10 Cys-NH₂ PL-1893 ReO[V] Ac-D-Phg-L-His-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 78 52 PL-1894 ReO[V] Ac-D-Ala-L-Phg-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 81 37 PL-1895 ReO[V] Ac-D-Ala-L-Phe-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 63 19 PL-1896 ReO[V] Ac-D-Nle-L-His-L-Cys-D-(NMe)Phe-L-Arg-L-Trp-NH₂ 1 −1 56 PL-1897 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Tiq-L-Arg-D-Trp-L-Cys-NH₂ 1 −24 12 PL-1899 ReO[V] C₆H₅(CH₂)₃-CO-L-Ser(Bzl)-D-(NMe)-Phe-L-Arg-D- 1 0 19 Trp-L-Cys-NH₂ PL-1900 ReO[V] 3-Bromophenyl acetyl-L-Lys-L-Ala-D-Trp-L-Cys- 1 47 10 L-Trp-NH₂ PL-1901 ReO[V] 3-Bromophenyl acetyl-L-Lys-L-Ala-D-Phe-L-Cys-L- 1 51 26 Trp-NH₂ PL-1902 ReO[V] 3-Bromophenyl acetyl-L-Lys-L-Ala-D-Phe(4-Me)-L- 1 93 17 Cys-L-Trp-NH₂ PL-1903 ReO[V] 3-Bromophenyl acetyl-L-Lys-L-Ala-D-Phe(3-Cl)-L- 1 71 5 Cys-L-Trp-NH₂ PL-1904 ReO[V] 3-Bromophenyl acetyl-L-Lys-L-Ala-D-HPhe-L-Cys-L- 1 11 2 Trp-NH₂ PL-1905 ReO[V] 2-Chlorophenyl acetyl-L-Lys-L-Ala-D-Phe(4-Cl)-L- 1 86 31 Cys-L-Trp-NH₂ PL-1906 ReO[V] 4-Chlorophenyl acetyl-L-Lys-L-Ala-D-Phe(4-Cl)-L- 1 91 68 Cys-L-Trp-NH₂ PL-1907 ReO[V] 4-Methylphenyl acetyl-L-Lys-L-Ala-D-Phe(4-Cl)-L- 1 69 44 Cys-L-Trp-NH₂ PL-1908 ReO[V] Indonyl acetyl-L-Lys-L-Ala-D-Phe(4-Cl)-L-Cys-L-Trp- 1 33 8 NH₂ PL-1909 ReO[V] 3-Bromophenyl acetyl-L-Arg-L-Ala-D-Phe(4-Cl)-L- 1 95 32 Cys-L-Trp-NH₂ PL-1910 ReO[V] Heptanoyl-L-Dpr(Bz)-D-Phe(2-Cl)-L-Arg-D-Trp-L- 1 23 42 Cys-NH₂ PL-1911 ReO[V] Heptanoyl-L-Dpr(2′-Naphthalene acetyl)-D-Phe(2- 1 −6 11 Cl)-L-Arg-D-Trp-L-Cys-NH₂ PL-1912 ReO[V] Heptanoyl-L-Dpr(1′-Adamantane carbonyl)-D-Phe(2- 1 −3 2 Cl)-L-Arg-D-Trp-L-Cys-NH₂ PL-1913 ReO[V] Heptanoyl-L-Dpr(4′-MePhenyl acetyl)-D-Phe(2-Cl)-L- 1 22 35 Arg-D-Trp-L-Cys-NH₂ PL-1914 ReO[V] Heptanoyl-L-Dpr(3′-BrPhenyl acetyl)-D-Phe(2-Cl)-L- 1 20 53 Arg-D-Trp-L-Cys-NH₂ PL-1915 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(2-Cl)$$-L-Arg-L-Trp-L- 1 94 72 Cys-NH₂ PL-1916 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(2-Cl)-L-Arg-L-His-L- 1 9 44 Cys-NH₂ PL-1917 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(2-Cl)-L-Arg-L-Nal 2′-L- 1 94 48 Cys-NH₂ PL-1918 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(2-Cl)-L-Arg-L-Bip-L- 1 10 21 Cys-NH₂ PL-1919 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(2-Cl)-L-Arg-L-Pal 3′-L- 1 17 47 Cys-NH₂ PL-1920 ReO[V] D-Phe-L-Arg-L-Trp-L-Cys-NH₂ 1 52 65 PL-1921 ReO[V] Ac-D-Phe-L-Arg-L-Trp-L-Cys-NH₂ 1 20 25 PL-1922 ReO[V] Ac-L-Nle-D-Phe-L-Arg-L-Trp-L-Cys-NH₂ 1 25 28 PL-1923 ReO[V] Ac-L-Nle-L-Ala-D-Phe-L-Arg-L-Trp-L-Cys-NH₂ 1 68 70 PL-1924 ReO[V] Ac-L-Pro-D-Phe-L-Arg-L-Trp-L-Cys-NH₂ 1 44 33 PL-1925 ReO[V] Heptanoyl-D-Phe-L-Arg-L-Trp-L-Cys-NH₂ 1 6 18 PL-1926 ReO[V] Bz-L-Arg-L-Trp-L-Cys-NH₂ (SEQ ID NO: 69) 1 7 25 PL-1927 ReO[V] Phenyl acetyl-L-Arg-L-Trp-L-Cys-NH₂ 1 8 28 PL-1928 ReO[V] 3-Phenyl-propanoyl-L-Arg-L-Trp-L-Cys-NH₂ 1 8 32 PL-1929 ReO[V] 4-Phenyl-butanoyl-L-Arg-L-Trp-L-Cys-NH₂ 1 2 18 PL-1930 ReO[V] t-Cinnamoyl-L-Arg-L-Trp-L-Cys-NH₂ 1 −20 9 PL-1931 ReO[V] 1-Naphthyl-acetyl-L-Arg-L-Trp-L-Cys-NH₂ 10 92 47 PL-1932 ReO[V] 2-Naphthyl-acetyl-L-Arg-L-Trp-L-Cys-NH₂ 1 1 16 PL-1933 ReO[V] 1-Naphthoyl-L-Arg-L-Trp-L-Cys-NH₂ 1 0 14 PL-1934 ReO[V] 2-Naphthoyl-L-Arg-L-Trp-L-Cys-NH₂ 1 6 34 PL-1935 ReO[V] Heptanoyl-L-Arg-L-Trp-L-Cys-NH₂ 1 8 39 PL-1936 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(4-F)-L-Arg-L-Trp-L-Cys- 1 81 71 NH₂ PL-1937 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(penta-F)-L-Arg-L-Trp-L- 1 91 65 Cys-NH₂ PL-1938 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Pal(2)-L-Arg-L-Trp-L-Cys- 1 16 16 NH₂ PL-1939 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(2-Br)-L-Arg-L-Trp-L- 1 91 73 Cys-NH₂ PL-1940 ReO[V] Ac-D-Ala-L-Nle-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 89 26 PL-1941 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(2-Cl)-L-Lys-L-Nal 2-L- 1 90 25 Cys-NH₂ PL-1942 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(2-Cl)-L-Arg-L-Nal 1-L- 1 53 16 Cys-NH₂ PL-1943 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(penta-F)-L-Arg-L-Nal 2- 1 93 64 L-Cys-NH₂ PL-1944 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(penta-F)-L-Lys-L-Nal 2- 1 80 40 L-Cys-NH₂ PL-1945 ReO[V] Heptanoyl-L-Hyp(Bzl)-D-Phe(2-Cl)-L-Arg-L-Nal 2-L- 1 94 30 Cys-NH₂ PL-1946 ReO[V] Heptanoyl-[(2S,3R),5-phenyl pyrrolidinyl-2-carbonyl]- 1 81 24 D-Phe(2-Cl)-L-Arg-L-Nal 2-L-Cys-NH₂ PL-1947 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(4-CF₃)-L-Arg-L-Trp-L- 1 98 23 Cys-NH₂ PL-1948 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(4-CH₃)-L-Arg-L-Trp-L- 1 98 50 Cys-NH₂ PL-1949 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(4-Cl)-L-Arg-L-Trp-L- 1 99 77 Cys-NH₂ PL-1950 ReO[V] Heptanoyl-L-Ser(Bzl)-D-Phe(3-Cl)-L-Arg-L-Trp-L- 1 92 37 Cys-NH₂ PL-1951 ReO[V] Ac-D-Val-L-His-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 60 32 PL-1952 ReO[V] Ac-D-Ala-L-Chg-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 88 46 PL-- ReO[V] Ac-D-Ala-L-Val-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 69 19 1953 PL-1955 ReO[V] Ac-D-Chg-L-His-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 76 68 PL-1956 ReO[V] Ac-D-Cha-L-His-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 58 64 PL-1957 ReO[V] Ac-D-Leu-L-His-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 66 53 PL-1958 ReO[V] Ac-D-Val-L-Phg-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 60 31 PL-1959 ReO[V] Ac-D-Chg-L-Phg-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp- 1 55 27 NH₂ PL-1960 ReO[V] Ac-D-Cha-L-Phg-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp- 1 38 16 NH₂ PL-1961 ReO[V] Ac-D-Leu-L-Phg-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 77 38 PL-1962 ReO[V] Ac-D-Val-L-Phe-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 47 23 PL-1963 ReO[V] Ac-D-Chg-L-Phe-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp- 1 31 27 NH₂ PL-1964 ReO[V] Ac-D-Cha-L-Phe-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp- 1 28 38 NH₂ PL-1965 ReO[V] Ac-D-Leu-L-Phe-L-Cys-D-Phe(2-Cl)-L-Arg-L-Trp-NH₂ 1 62 46 PL-1970 ReO[V] Phenylacetyl-L-Arg-L-Ala-D-Phe(4-Cl)-L-Cys-D-Trp- 1 92 51 NH₂ PL-1971 ReO[V] 3′-bromophenylacetyl-L-Arg-D-Ala-Dphe(4-Cl)-L- 1 33 67 Cys-L-Trp-NH₂ PL-1972 ReO[V] Phenylacetyl-D-Arg-L-Ala-D-Phe(4-Cl)-L-Cys-L-Trp- 1 17 27 NH₂

For selected peptides of this invention, a cAMP assay was also performed, with results as shown in Table 2. Human MC4-R or B-16 cells were grown to confluence in 96 well plates (plating approximately 250,000 cells per well). Identical sets of cells in triplicate were treated with 0.2 mM isobutylmethylxanthine (IBMX) and the chosen concentration of the rhenium metal ion-complexed peptide and the rhenium metal ion-complexed peptide in the presence of 20 nM α-MSH. Cells similarly treated but with only 20 nM α-MSH served as positive control. A buffer blank, as a negative control, was also included. Incubation was for one hour at 37° C. after which the medium was aspirated and the cells extarted with 150 microliters of HCl. Total cAMP accumulated in 100 microliters of this solution was quantitated using a commercially available low pH cAMP assay kit (R&D Systems) by the procedure specified by the kit supplier. The table shows the amount of cAMP accumulated in the cells upon exposure to the test compound alone and the presence of 20 nM α-MSH. The rhenium metal ion-complexed peptide showing cAMP accumulation in the same range as or higher than the positive control (buffer blank in the presence of α-MSH) are considered to be agonist ligands. The rhenium metal ion-complexed peptide showing accumulation in the same range as the negative control (buffer blank in the absence of α-MSH) are ineffective at the test concentration if the result is similar to the positive control where alpha-MSH is also present in the assay. The rhenium metal ion-complexed peptide showing accumulation in the same range as the negative control are considered to be antagonists if there is inhibition in cAMP when α-MSH is present in the assay. Values above the positive control are due to potent agonism, experimental variance or synergistic agonistic effects of rhenium metal ion-complexed peptide and α-MSH. TABLE 2 Evaluation of MC-specific metallopeptides of the primary structure of Table 1 in cAMP stimulation assay in presence and absence of natural stimulator α-MSH cAMP Accumulation (pMol/ml) METAL μM Absence of Presence of ID ION Concentration α-MSH α-MSH Buffer blank 1 99 PL-815 ReO[V] 10 55 178 PL-836 ReO[V] 10 0.31 68 PL-837 ReO[V] 10 9 63 PL-838 ReO[V] 10 2 53 PL-1102 ReO[V] 10 2 113 PL-1113 ReO[V] 10 123 67 PL-1145 ReO[V] 10 221 277 PL-1160 ReO[V] 10 18 34 PL-1165 ReO[V] 10 15 71 PL-1179 ReO[V] 10 7 50 PL-1183 ReO[V] 1 42 39 PL-1185 ReO[V] 1 30 22 PL-1189 ReO[V] 1 52 34 PL-1190 ReO[V] 1 63 148 PL-1191 ReO[V] 1 8 94 PL-1207 ReO[V] 1 4 3 PL-1208 ReO[V] 10 2 2 PL-1209 ReO[V] 1 5 13 PL-1210 ReO[V] 1 8 5 PL-1211 ReO[V] 1 10 8 PL-1222 ReO[V] 50 177 346 PL-1223 ReO[V] 10 63 85 PL-1233 ReO[V] 10 19 21 PL-1235 ReO[V] 10 29 28 PL-1236 ReO[V] 10 11 30 PL-1237 ReO[V] 10 96 116 PL-1238 ReO[V] 10 26 140 PL-1239 ReO[V] 10 108 131 PL-1249 ReO[V] 10 4 139 PL-1250 ReO[V] 10 2 15 PL-1251 ReO[V] 10 7 21 PL-1255 ReO[V] 10 2 2 PL-1256 ReO[V] 1 17 71 PL-1258 ReO[V] 10 9 63 PL-1259 ReO[V] 1 131 131 PL-1260 ReO[V] 1 5 6 PL-1261 ReO[V] 1 189 214 PL-1264 ReO[V] 1 1 11 PL-1265 ReO[V] 1 3 127 PL-1266 ReO[V] 1 2 131 PL-1268 ReO[V] 1 18 16 PL-1269 ReO[V] 1 4 2 PL-1270 None 1 139 123 PL-1272 None 1 80 75 PL-1276 ReO[V] 1 3 12 PL-1281 ReO[V] 1 158 25 PL-1285 ReO[V] 1 148 158 PL-1292 ReO[V] 1 3 13 PL-1293 ReO[V] 1 3 6 PL-1294 ReO[V] 1 43 91 PL-1295 ReO[V] 1 136 122 PL-1298 ReO[V] 1 1 32 PL-1297 ReO[V] 1 3 7 PL-1301 ReO[V] 1 1 23 PL-1302 ReO[V] 1 12 43 PL-1303 ReO[V] 1 2 59 PL-1305 ReO[V] 1 2 3 PL-1306 ReO[V] 1 189 158 PL-1329 ReO[V] 1 1 63 PL-1332 ReO[V] 1 0 103 PL-1335 ReO[V] 1 0 3 PL-1340 ReO[V] 1 3 7 PL-1342 ReO[V] 10 43 59 PL-1346 ReO[V] 10 3 76 PL-1347 ReO[V] 10 2 81 PL-1351 ReO[V] 10 68 30 PL-1370 ReO[V] 1 2 16 PL-1372 ReO[V] 1 13 149 PL-1373 ReO[V] 1 1 8 PL-1374 ReO[V] 1 37 73 PL-1387 None 1 52 94 PL-1396 ReO[V] 1 36 120 PL-1438 ReO[V] 1 113 126 PL-1440 ReO[V] 1 59 55 PL-1443 ReO[V] 1 4 34 PL-1451 ReO[V] 1 9 90 PL-1493 ReO[V] 1 4 15 PL-1581 ReO[V] 1 111 132 PL-1658 ReO[V] 1 10 67 PL-1659 ReO[V] 1 7 78 PL-1662 ReO[V] 1 6 96 PL-1663 ReO[V] 1 55 122 PL-1664 ReO[V] 1 7 44 PL-1665 ReO[V] 1 10 70 PL-1666 ReO[V] 1 15 28 PL-1667 ReO[V] 1 23 63 PL-1684 ReO[V] 1 5 110 PL-1685 ReO[V] 1 7 102 PL-1686 ReO[V] 1 4 106 PL-1690 ReO[V] 1 13 76 PL-1691 None 1 30 102 PL-1692 None 1 18 106 PL-1694 ReO[V] 1 25 92 PL-1695 ReO[V] 1 30 101 PL-1702 ReO[V] 1 4 134 PL-1703 ReO[V] 1 2 73 PL-1704 ReO[V] 1 3 73 PL-1705 ReO[V] 1 2 74 PL-1706 ReO[V] 1 2 71 PL-1707 ReO[V] 1 15 156 PL-1708 ReO[V] 1 13 54 PL-1709 ReO[V] 1 33 46 PL-1710 ReO[V] 1 3 7 PL-1718 ReO[V] 1 23 105 PL-1722 ReO[V] 1 28 180 PL-1723 ReO[V] 1 30 169 PL-1726 ReO[V] 1 21 171 PL-1727 ReO[V] 1 27 151 PL-1728 ReO[V] 1 15 164 PL-1730 ReO[V] 1 22 111 PL-1731 ReO[V] 1 19 117 PL-1732 ReO[V] 1 14 105 PL-1733 ReO[V] 1 16 114 PL-1734 ReO[V] 1 13 122 PL-1735 ReO[V] 1 20 115 PL-1736 ReO[V] 1 17 152 PL-1737 ReO[V] 1 53 162 PL-1738 ReO[V] 1 7 173 PL-1751 ReO[V] 1 71 96 PL-1752 ReO[V] 1 4 101 PL-1753 ReO[V] 1 39 104 PL-1754 ReO[V] 1 3 100 PL-1755 ReO[V] 1 21 110 PL-1756 ReO[V] 1 43 102 PL-1757 ReO[V] 1 11 96 PL-1758 ReO[V] 1 34 61 PL-1759 ReO[V] 1 24 79 PL-1760 ReO[V] 1 66 80 PL-1761 ReO[V] 1 11 87 PL-1762 ReO[V] 1 49 88 PL-1774 ReO[V] 1 48 163 PL-1775 ReO[V] 1 53 170 PL-1776 ReO[V] 1 26 138 PL-1778 ReO[V] 1 50 141 PL-1779 ReO[V] 1 47 155 PL-1780 ReO[V] 1 8 126 PL-1782 ReO[V] 1 7 108 PL-1788 ReO[V] 1 189 109 PL-1789 ReO[V] 1 96 90 PL-1790 ReO[V] 1 164 149 PL-1791 ReO[V] 1 163 137 PL-1792 ReO[V] 1 187 109 PL-1793 ReO[V] 1 119 98 PL-1794 ReO[V] 1 4 133 PL-1795 ReO[V] 1 71 124 PL-1796 ReO[V] 1 4 133 PL-1799 ReO[V] 1 9 117 PL-1801 ReO[V] 1 42 107 PL-1805 ReO[V] 1 15 78 PL-1806 ReO[V] 1 10 110 PL-1807 ReO[V] 1 103 115 PL-1808 ReO[V] 1 109 137 PL-1809 ReO[V] 1 113 130 PL-1810 ReO[V] 1 101 125 PL-1811 ReO[V] 1 117 66 PL-1812 ReO[V] 1 132 93 PL-1813 ReO[V] 1 36 91 PL-1814 ReO[V] 1 8 80 PL-1815 ReO[V] 1 34 119 PL-1816 ReO[V] 1 69 89 PL-1817 ReO[V] 1 24 110 PL-1818 ReO[V] 1 6 96 PL-1819 ReO[V] 1 93 96 PL-1820 ReO[V] 1 8 102 PL-1821 ReO[V] 1 37 88 PL-1822 ReO[V] 1 13 101 PL-1823 ReO[V] 1 14 114 PL-1824 ReO[V] 1 71 124 PL-1825 ReO[V] 1 4 133 PL-1825 ReO[V] 1 7 106 PL-1838 ReO[V] 1 16 65 PL-1839 ReO[V] 1 63 77 PL-1840 ReO[V] 1 76 77 PL-1841 ReO[V] 1 91 81 PL-1842 ReO[V] 1 25 76 PL-1843 ReO[V] 1 18 81 PL-1844 ReO[V] 1 110 81 PL-1845 ReO[V] 1 82 38 PL-1877 ReO[V] 1 72 125 PL-1879 ReO[V] 1 75 108 PL-1880 ReO[V] 1 16 92 PL-1883 ReO[V] 1 125 115 PL-1884 ReO[V] 1 108 158 PL-1885 ReO[V] 1 135 148 PL-1886 ReO[V] 1 151 161 PL-1900 ReO[V] 1 19 87 PL-1902 ReO[V] 1 56 143 PL-1903 ReO[V] 1 62 108 PL-1905 ReO[V] 1 59 96 PL-1906 ReO[V] 1 68 87 PL-1907 ReO[V] 1 62 98 PL-1909 ReO[V] 1 70 81 PL-1915 ReO[V] 1 123 128 PL-1917 ReO[V] 1 109 116 PL-1931 ReO[V] 10 15 79 PL-1144 ReO[V] 10 215 280 PL-1489 ReO[V] 1 9 16 PL-1605 ReO[V] 1 16 15

Based on the foregoing studies, potential lead molecules have been identified, including the following: PL-1145 MC1-R agonist (Template 2) PL-1144 MC1-R agonist (Template 2) PL-1493 MC4-R antagonist (Template 1) PL-1883 MC4-R agonist (Template 1) PL-1489 MC4-R antagonist (Template 5) PL-1950 MC4-R specific (Template 5) PL-1947 MC4-R specific (Template 5) PL-1581 Non-specific agonist (Template 5) PL-1790 Non-specific agonist (Template 5) PL-1791 Non-specific agonist (Template 5) PL-1792 Non-specific agonist (Template 5) PL-1605 Non-specific antagonist (Template 6) PL-1758 Non-specific (Template 4) PL-1877 MC4-R specific (Template 4) PL-1902 MC4-R specific (Template 4) PL-1909 MC4-R specific agonist (Template 4) PL-1888 MC4-R specific (Template 7) PL-1269 MC4-R specific antagonist (Template 3) PL-1297 MC4-R specific antagonist (Template 3)

Radiopharmaceutical Applications. In one embodiment, metallopeptides of this invention that are MC1-R specific can be used, when complexed to ^(99m)Tc as a radiodiagnostic agent, for imaging melanoma tumor metastases, and when complexed to rhenium-188 (¹⁸⁸Re), rhenium-186 (¹⁸⁶Re) or other therapeutic radionuclides as a radiotherapeutic agent for treatment of melanoma tumors and metastatic tumors.

Human melanoma has a complex antigenic profile. It is generally believed that malignant melanoma is derived by UV activity from DOPA positive melanocytes, the melanin (skin pigment) producing units. Primary diagnosis involves electron microscopic examination to reveal the presence or absence of pre-melanosomes. Melanotic melanoma is classified as dendritic, spindle, bizarre, large epitheloid, small nevus and so on. Amelanotic melanoma, on the other hand, is frequently misdiagnosed because the histology of these cells resembles that of malignant lymphoma, carcinoma or sarcoma. Therefore, morphological evaluation may not prove reliable for clinical diagnosis. Thus, there is a need for a receptor-specific diagnostic test, particularly to identify and locate metastatic melanoma tumors.

Several studies have documented the presence of melanotropin receptors on primary human melanoma cells. Melanotropin receptors have been reported as markers for melanotic and amelanotic human melanoma tumors. In particular, the presence of MC1-R has been demonstrated in human melanoma cells by an antibody to MC1-R.

The melanotropin bioactive sequence, or message segment, is a tetrapeptide, His-Phe-Arg-Trp (SEQ ID NO:1), that exist as a reverse turn. Within the reverse turn, the His, Phe, and Trp residues have been postulated to form a hydrophobic receptor binding surface. The His residue has recently been identified as a signal residue that helps discriminate between MC1-R and MC4-R. Thus, it is possible to design metallopeptides of this invention which are specific for MC1-R, and bind MC1-R with high affinity, but which are not specific for MC4-R, or which bind MC4-R with low affinity. One result is a ^(99m)Tc-labeled radioimaging agent with high specific affinity and selectivity for the MC1-R. In addition, both agonists and antagonists metallopeptides of this invention are contemplated for comparative evaluation in imaging melanoma tumors.

The product can be formulated as a single-vial, lyophilized radiolabeling kit containing the peptide in an uncomplexed state, buffer, and a reducing agent for pertechnetate. To induce radiolabeling, resulting in a metallopeptide, the vial is incubated after the addition of sodium pertechnetate.

In one method of labeling with ^(99m)Tc, a 5-10 μg sample of the peptide taken in 0.001 N aq. HCl is mixed with 1-30 mCi of generator-eluted Na^(99m)TcO₄ in a 5 ml serum vial. The volume of the resulting mixture is adjusted to 600 μl using injectable saline. A 400 μl volume of freshly prepared and nitrogen-purged phthalate-tartrate-Sn(II) buffer (40:10:1 mM) is added to the vial under a nitrogen head space. The vial is immediately sealed and placed in a shielded boiling water bath. After 15 minutes the vial is removed from the water bath and allowed to come to room temperature. The radiochemical purity, as calculated from HPLC profiles, ranges from 90-99%.

The peptides of this invention may alternatively be labeled with ^(99m)Tc by other means, including use of stannous-tartrate-succinate buffer, stannous-EDTA-succinate buffer, stannous stabilized in glucoheptonate, or a stannous-borate-tartrate buffer, as well as other means of labeling with ^(99m)Tc known in the art.

For radiopharmaceutical and other medical applications, the metallopeptides of this invention may be delivered to a subject by any means known in the art. This includes intravenous injection, subcutaneous injection, administration through mucous membranes, oral administration, dermal administration, regional administration to an organ, cavity or region, and the like.

Imaging may be any means known in the art, including gamma camera and SPECT imaging. Imaging may commence immediately after administration, and may include time course radiographic studies, and imaging may continue so long as images may be obtained.

The MC1-R specific metallopeptides of this invention may be used as melanoma specific tumor imaging and staging agent. These uses include early detection and localization of primary and disseminated lesions, identification of lymph nodes containing lesions, radioimmunoguided surgery applications and the like. Tumor imaging using a ^(99m)Tc-labeled metallopeptide of this invention selective for the MC1-R will further help in formulating the optimal clinical treatment modality, whether surgical, radiation or chemotherapeutic.

Chemoprevention Applications. In another embodiment, metallopeptides of this invention that are MC1-R specific can be used as chemoprevention agents against sun-induced, such as by UV radiation, neoplastic activity in human skin. MC1-R agonist metallopeptides of this invention may be employed to stimulate epidermal melanocytes to produce melanin as well as to convert pheomelanin to eumelanin. Eumelanin, which is dark brown or black pigmentation, is considered more photo-protective than pheomelanin, which is yellow or red pigmentation.

In general, darker skinned individuals have lower incidences of skin cancer than lighter skinned people. The dark pigment eumelanin, a brown/black pigment incorporating dopa-based structural units, is the main photoprotective agent in skin. Lighter colored people have higher levels of pheomelanin, a red/yellow pigment having predominantly cysteine and related sulfur-based structural units, which is an inefficient UV absorber. The process of melanogenesis is believed to involve stimulation of MC1-R in epidermal melanocytes, thereby mediating the stimulation of tyrosinase enzymes within these pigment cells, inducing the conversion of tyrosine to dopa and then through dopaquinone to eumelanin. Sun tanning due to direct sun exposure is also proposed to result from the same pathway by local production of melanotropic peptide from a POMC gene in the epidermis. Thus stimulation of eumelanin production and conversion of pheomelanin to eumelanin may be a desirable chemoprevention modality in blocking sun, or UV, induced neoplastic activity in skin.

A potent, high-affinity and highly selective MC1-R agonist metallopeptide of this invention can accordingly be used as a therapeutic chemoprevention agent for combating harmful sun, or UV, exposure that induces neoplastic activity in skin melanocytes.

Particularly for individuals previously diagnosed with melanoma or diagnosed as highly susceptible to melanoma, avoidance of any significant UV exposure is medically necessary. Currently, both physical screens, such as hats, long sleeves and so on, and various sun- or UV-protecting creams and formulations are utilized. However, the efficacy, both absolute and as a function of time, of even the best chemical sun block is limited, and physical screens are inappropriate for many activities. This results in individuals either receiving unacceptably high UV doses or foregoing normal activities, such as swimming, hiking, skiing, attending sporting events, employment in outdoor settings and so on.

Eumelanin production through activation of the MC1-R on epidermal melanocytes provides a better natural shield against sun (UV) induced mutations and DNA damage than does any chemical sun block. Eumelanin is a better UV absorber over a wide range than any commercially available sun-protecting cream or formulation.

The metallopeptides for this application may be made with non-radioactive isotopes of rhenium, or other metals as specified herein, with metal ion complexation by any means specified herein or known in the art. The metallopeptides may be formulated by any means known in the art, including but not limited to tablets, capsules, caplets, suspensions, powders, lyophilized forms and aerosols and may be mixed and formulated with buffers, binders, stabilizers, anti-oxidants and other agents known in the art. The metallopeptides may be administered by any systemic or partially systemic means known in the art, including but not limited to intravenous injection, subcutaneous injection, administration through mucous membranes, oral administration, dermal administration, skin patches, aerosols and the like.

Therapeutic Applications. In another embodiment, metallopeptides of this invention that are MC4-R agonists can be used as a therapeutic agent to modify energy metabolism and feeding behavior, including treatment of pathological obesity and related conditions. Metallopeptides of this invention that are MC4-R antagonists can also be used as a therapeutic agent in eating disorders, such as treatment of anorexia.

Control centers for eating and satiety reside in the hypothalamus. These responses are determined by diverse hormones and soluble factors that signal through specific receptors in the hypothalamus. MC4-R is known to be expressed in the brain, and inactivation of this receptor by gene targeting has resulted in mice with the maturity-onset obesity syndrome that is associated with hyperphagia, hyperinsulinemia and hyperglycemia.

In yet another embodiment, metallopeptides of this invention may used as therapeutic agents for treatment of sexual dysfunction, including treatment of both male erectile dysfunction and female sexual dysfunction. In yet another embodiment, metallopeptides of this invention may be used as therapeutic agents for treatment of inflammation, including specifically MC1-R and MC3-R agonist metallopeptides.

The metallopeptides for this application may be made with non-radioactive isotopes of rhenium, or other metals as specified herein, with metal ion complexation by any means specified herein or known in the art. The metallopeptides may be formulated by any means known in the art, including but not limited to tablets, capsules, caplets, suspensions, powders, lyophilized forms and aerosols and may be mixed and formulated with buffers, binders, stabilizers, anti-oxidants and other agents known in the art. The metallopeptides may be administered by any systemic or partially systemic means known in the art, including but not limited to intravenous injection, subcutaneous injection, administration through mucous membranes, oral administration, dermal administration, skin patches, aerosols and the like.

The invention is further illustrated by the following non-limiting examples.

EXAMPLE 1 Development of a Prototype Metallopeptide Library for the Melanocortin Receptor

The library design was based on the tetrapeptide message sequence, His-Phe-Arg-Trp (6-9 sequence) (SEQ ID NO:1), of α-MSH. This sequence exists as a reverse turn, making it suitable for conversion into a metallopeptide format of this invention. In this approach metallopeptides were designed around a tripeptide N₃S₁ MBD designed for a rhenium metal ion. The MBD was derivatized to yield the pentapeptide Ac-His-Phe-Arg-Cys-Trp-NH₂ (SEQ ID NO:8) as a putative candidate for melanocortin (“MC”) receptors. Further refinements in the structure were made in response to other considerations, including the chirality of amino acid side chains, yielding a template structure Ac-His-D-Phe-Arg-Cys-Trp-NH₂. The structure of this peptide after binding to rhenium is:

The template structure was used to define a small combinatorial library utilizing split synthesis methodologies. The final template selected for the combinatorial library was Ac-D-His-Xaa-D-Cys-Trp-NH₂, where Xaa was D-(2′) Naphthylalanine, D-Trp, D-HomoPhe, or D-Phenylglycine. For this library, the peptide resin, Cys(S^(t)Bu)-Trp(Boc)-Resin was split in four equal parts. Each part was reacted with one of the four Xaa types. After coupling, the resin pools were mixed and synthesis continued in a single pool to couple the His residue. The final result was four separate peptides in a single pool, each peptide varying by one amino acid, in the Xaa position.

An S^(t)Bu OSPG group was used to protect the SH group during synthesis. After solid-phase assembly of the peptide chain using Fmoc chemistry with acid labile side chain protecting groups, the S^(t)Bu group was split using tributylphosphine. The resulting free SH-containing peptide-resin was treated with the rhenium transfer agent Re(O)Cl₃(PPh₃)₂ in the presence of 1,8-Diazabicyclo[5,4,0]undec-7-ene as base. The resulting metallopeptide resin was then treated with TFA to cleave it from the resin and de-protect all the side chain protecting groups. The products were analyzed by mass spectrometry. HPLC analysis was performed and individual peaks collected and subjected to mass analysis. The resulting peptides were analyzed by electron spray mass spectrometry, yielding the predicted mass, including the rhenium complexed to the peptide.

EXAMPLE 2 Design and Synthesis of Melanocortin Receptor-Specific Metallopeptide Library

The library was rationally designed based upon data relating to melanocortin receptors and peptide sequences specific to the melanocortin receptors, including melanotropin side-chain pharmacophores, D-Phe⁷ and Trp⁹, that interact with a hydrophobic network of receptor aromatic residues in transmembrane regions 4, 5, 6, and 7. Based on this design criterion, a pharmacophore for the melanocortin receptor was preliminarily defined, and a combinatorial library designed for identification of potent and receptor-selective agonists.

Based on the design criteria, the putative structure R-Aaa-Baa-L-Cys-Caa-NH₂ was selected, in which each of Aaa, Baa and Caa are selected from L- or D-isomers of 2-Nal (1), Phe (2), Trp (3), Tyr (4) and Ala (5), so that any one of the foregoing can be substituted for any one of Aaa, Baa or Caa. In the nomenclature adopted for the library design, the five amino acids were designated 1 through 5, with the isomerism conventionally notated, so that, for example, Baa₂L refers to L-Phe in the Baa position.

The terminal R group was selected from Ac, C₆H₅OOH, CH₃(CH₂)₅—COOH, C₆H₅CH═CH—COOH (trans) and Pyridine-3-carboxylate. The terminal R group represents a truncated amino acid, and offers additional structural diversity.

A pool and split library synthesis scheme was employed such that 5,000 separate compounds were synthesized, resulting in 200 final pools each containing 25 different compounds, with the compounds differing solely by the amino acids in the Aaa and Baa position. Using this methodology, binding characteristics relating to the Caa amino acid or R terminal group can be identified through inter-group comparison, thereby simplifying the deconvolution strategy.

The library synthesis steps are set forth in FIG. 8. The resin of step 1 was divided into 10 groups. At step 2 each of Caa₁L through Caa₅D were coupled to an individual resin group, and L-Cys was coupled to each resin group, resulting in 10 groups and 20 couplings. Each of the resin groups of step 2 was then divided into 10 sub-groups as shown at step 3 (with only one subgroup illustrated at step 3, and for each subgroup of step 3, each of Baa₁L through Baa₅D were coupled to one group within the subgroup, resulting in 100 groups in 10 subgroups and 100 couplings. For each subgroup of step 3, the five Baa_(x)L members and the five Baa_(x)D members were separately pooled in step 4, resulting in 20 subgroups, with each subgroup containing five different sequences differing by the Baa_(x) member. Each of the 20 subgroups of step 4 were then in step 5 divided into 10 groups (with only one shown for illustration purposes in FIG. 8), and for each subgroup, each of Aaa₁L through Aaa₅D were coupled to one group within the subgroup, resulting in 200 groups in 20 subgroups and 200 couplings. For each subgroup of step 5, the five Aaa_(x)L members and the five Aaa_(x)D members were separately pooled in step 6, resulting in 40 subgroups, with each subgroup containing twenty-five different sequences differing by the Baa_(x) and Aaa_(x) member. In step 7, each of the 40 subgroups of step 6 was divided into five groups, and each of R₁ through R₅ were coupled to one group within the subgroup, resulting in 200 groups in 40 subgroups, with each group containing 25 different sequences differing by the Baa_(x) and Aaa_(x) member.

Peptides were synthesized using Fmoc chemistry, with side chain functionalities protected using acid labile groups. The SH group of the Cys residue was protected by a S^(t)Bu OSPG cleavable in presence of both base and acid labile groups using tributylphosphine as the reducing agent. The peptide chain was assembled on the solid phase using 1-(1H-benzotriazole-1-yl)-1,1,3,3,-tetramethyluronium tetrafluoroborate (TBTU) as a coupling agent. The SH group was then selectively unprotected and rhenium metal ion complexed using the rhenium transfer agent Re(O)Cl₃(PPh₃)₂ in the presence of 1,8-Diazabicyclo[5,4,0]undec-7-ene (DBU) as base. In this manner, the metal-peptide complex was formed with the peptide chain still tethered to the solid support. The metallopeptide was then liberated from the solid support by treatment with TFA. This solid phase approach to metal ion complexation is fully compatible with split synthesis methodologies employed in combinatorial libraries.

The synthesis process was performed using commercial automated synthesizers. Multiple manual synthesizers (such as those commercially available from SynPep Corporation, Dublin, Calif.) allow parallel synthesis of ten peptides simultaneously.

Quality control protocols were employed as required, and include HPLC, mass spectral analysis, and amino acid analysis on each individual pool of 25 compounds. The presence of each of pool constituent is established by molecular ion mass spectral analysis. Negative ion mode electron spray (ES) and matrix-assisted laser desorption (MALDI) techniques were employed. Using mass spectral analysis, three different measures were made: (a) the presence of up to 25 individual compounds by molecular ion peak measurement (assuming different masses for each compound), (b) confirmation that the molecular ion peaks show complexation to a rhenium metal ion, and (c) absence of peaks with molecular masses corresponding to peptides uncomplexed with metal ion. Rhenium is a mixture of two isotopes that differ in mass by 2 units (186 and 188) with a relative abundance of these isotopes of 1:2. The molecular ion profile of a metallopeptide appears as two peaks that differ by 2 mass units with integrated area ratios of 1:2. Rhenium thus acts as an internal mass spectral reference for these metallopeptides. A spectral analysis of one such pool of 25 compounds synthesized by the methods of this claim is shown at FIG. 9. Five sets of two metallopeptides in this pool have similar masses due to the presence of the same amino acids assembled in different sequences. The relative intensities of the peaks is due to differential ionization of individual compounds in the pool and does not reflect the relative amounts in the mixture. Each pair of peaks with mass unit differences of 2 and relative ratios of 1:2 are due to the relative abundance of two stable isotopes of rhenium (Re-185 and Re-187). The spectral analysis did not reveal any free uncomplexed linear peptides, which would be approximately 197 to 199 mass units less than the corresponding metallopeptide, due to the absence of the rhenium-oxo core.

Amino acid analysis of each pool of 25 metallopeptides was also employed, and was used to determine the relative equimolar ratio of each of 25 compounds in a pool. The synthetic protocols of split synthesis were designed to assure equimolar amounts of pool constituents.

EXAMPLE 3 Screening of Melanocortin Receptor-Specific Library

Metallopeptide library pools are screened for MC4-R receptor and MC1-R receptor binding activity in high throughput screening assays. The MC receptor-binding assay uses membrane preparations from B16-F1 or B16-F10 melanoma cells as the source of MC receptor. Cell membranes prepared from MC4-R-expressing 293 cells and negative control, untransfected 293 cells, are substituted for B16-F1 or B16-F10 melanoma cell membranes in MC4-R specific binding assays. The MC receptor-binding assays use the Millipore Multi-Screen System and are performed in 96-well Millipore filter plates (Durapore, 0.45 mm porosity) pre-blocked with 0.5% bovine serum albumin in phosphate buffered saline. Cell membrane preparations (12.5 μg/well) are incubated with 0.4 nM ¹²⁵I-NDP-MSH in HEPES Buffer containing 0.2% bovine serum albumin. Non-specific binding is determined by addition of 10⁻⁶ M α-MSH or 10⁻⁷ M NDP-MSH. Metallopeptides to be tested are added to reaction wells at a final concentration of 1 mM. After incubation for 90 minutes at room temperature, the binding reaction is rapidly terminated by filtration to capture the membranes. Filters are washed 3 times with ice-cold PBS and air-dried. Individual filters are then punched from the plates and distributed into gamma counter tubes. Radioactivity associated with the membranes is determined in a Packard Cobra gamma counter. Specific binding is determined as the radioactivity in wells containing ¹²⁵I-NDP-MSH alone minus the radioactivity in wells containing 10⁻⁶M α-MSH. Test compounds are screened in duplicate wells and are considered to be active where 1 μM concentrations inhibit >50% of the specific binding. Standard curves of unlabeled NDP-MSH will be included on each plate as an internal assay control.

A commercially available cAMP kit (R&D Systems, DE0350, low pH) is employed to evaluate agonist potential of metallopeptides that bind to MC4-R. 293 cells stably transfected with hMC-4 receptor, or B16-F1 melanoma cells, are grown to confluence in 96-well dishes. Cells are washed and fresh RPMI containing 0.2 mM isobutylmethylxanthine (cAMP phosphodiesterase) and varying concentrations of metallopeptides, or α-MSH as a positive control, are added, and the cells are incubated for 1 hour at 37° C. Medium is aspirated, and cell layers extracted with 150 μl of 0.1 M HCl. Total cAMP accumulation in 100 μl of cell extract is quantitated in 96-well plates by competitive immunoassay with the cAMP kit, using an acetylation modification. EC₅₀ values for test compounds are calculated based on cAMP accumulation in cells treated with 10⁻⁶ M α-MSH. The capabilities of both of these cell types to accumulate cAMP in the presence of α-MSH and MSH analog peptides are documented in the scientific literature; see, for example, Ollman M M et al: Science 278:135-138, 1997.

EXAMPLE 4 Deconvolution of Melanocortin Receptor-Specific Library

Deconvolution of a positive pool is done by iterative re-synthesis and screening deconvolution approaches. The individual 25 constituents are synthesized separately, or alternatively in 5 smaller pools of 5 compounds each, with each pool screened in receptor binding assays. The latter approach is preferred where there is a high hit frequency in the preliminary screen. The compounds in pools with the best results (closest to receptor affinity in the nanomolar range and MC4-R to MC1-R selectivity of at least 100) are individually synthesized and screened.

EXAMPLE 5 Alternative Method of Deconvolution of Melanocortin Receptor-Specific Library

In this example, an alternative method of mass spectral deconvolution of metallopeptide libraries is employed. The method is based on the internal signature of rhenium-complexed peptides (two isotopic peaks in 1:2 ratios differing by 2 mass units), which generally permits metallopeptide identification even in mixed solutions. A positive pool is incubated with receptor-bearing cells, the excess unbound compounds washed away under controlled conditions, and the cells treated with a solvent to disrupt metallopeptide binding and extract the metallopeptide in the solvent. Mass spectral analysis of the solvent reveals the metallopeptide or metallopeptides which are bound to the receptor-bearing cells, and through comparison to the quality control data it is possible to ascertain the specific metallopeptide or metallopeptides which are bound. This process provides high throughput of metallopeptide library screening.

EXAMPLE 6 Single Pot Synthesis of a Library of Four Metallopeptides of the General Structure Ac-His-Xaa-Cys-Trp-NH₂

A synthesis procedure similar to that described in Example 1 was used in making this library. A NovaSyn TGR resin for making peptide amides (substitution 0.2 mM/gm) was used. Fmoc synthetic strategy was employed using the following protected amino acids: Fmoc-Trp(Boc), Fmoc-Cys(S^(t)Bu), Fmoc-Xaa, and Fmoc-His(Trityl). The Xaa amino acids were Trp, HomoPhe, 2′-Naphthylalanine, and Phenylglycine. The peptide resin Cys(S^(t)Bu)-Trp-NH₂ was split into four equal pools and one of the Xaa amino acids was coupled to one individual pool. After completion of the coupling reaction, the four resin pools were mixed again. The synthesis proceeded with the coupling of His followed by acetylation of the N-terminus. After the complete assembly of the peptide chain Ac-His(Trt)-Xaa-Cys(S^(t)Bu)-Trp(Boc)-NH₂, the S^(t)Bu group was removed by treatment with DMF/tributylphosphine and rhenium-oxo metal ion was complexed as generally described above. The fully protected metallopeptide was deblocked and liberated from the solid support by treatment with a cleavage cocktail (95:5 mixture of trifluoroacetic acid-triisopropylsilane) for three hours. The metallopeptide library was recovered by precipitation using cold ether. The resulting pellet was washed twice and 0.5 ml of 95% acetic acid was added. After one-half hour 5 ml of water was added and the solution was freeze-dried yielding the desired library in solid form. Mass spectrometric analysis of the library pool confirmed the correct masses for all four members of the library: TABLE 3 Compound Structure Calculated Mass Mass (M + 1) found 1 Ac-His-Phg-Cys-Trp-NH₂ 815.7 and 817.6 815.2 and 816.7 (SEQ ID NO: 6) 2 Ac-His-Trp-Cys-Trp-NH₂ 868.8 and 870.7 868.0 and 870.1 (SEQ ID NO: 3) 3 Ac-His-HPhe-Cys-Trp-NH₂ 843.8 and 845.7 842.8 and 845.2 (SEQ ID NO: 4) 4 Ac-His-2′-Nal-Cys-Trp-NH₂ 880.0 and 881.9 879.1 and 880.9 (SEQ ID NO: 5)

As noted in Table 3, two molecular ion peaks differing in mass units of 2 were calculated and observed for each structure; this difference is presumptively due to the presence of two natural isotopes of rhenium, Re-185 and Re-187, in the complexation step. In addition, the area under the observed peaks in the spectrometric analysis showed that for each structure the area was in a 1:2 ratio, which is identical to and presumptively related to the relative abundance of Re-185 and Re-187 isotopes. These results confirmed the complexation of rhenium to the peptides. The spectral analysis is shown at FIG. 10.

These results were also confirmed by HPLC analysis of this library of four compounds, which results were compared to HPLC analysis of each of the four individual members performed under identical HPLC conditions. As is evident from FIG. 11A, each of the four member components is present in the library mixture. In the HPLC profile each of the metallopeptide has resolved into two isomers due to alternate orientations (syn and anti) of the rhenium oxo core. The HPLC analysis also revealed the lack of uncomplexed linear peptides in the preparation. All four compounds used for this comparison were individually prepared using methods identical to that described above for synthesis of the library. The HPLC profiles are shown as FIGS. 11B to 11E.

EXAMPLE 7 Synthesis of MC1-R Specific Metallopeptides for Use as Chemoprevention Agent

High potency metallopeptides are also provided with N-terminal modifications. Systematic N-terminal modifications are made based upon the limited data available in the literature related to receptor-binding affinities of peptide analogs for various MC receptor types. In general, these studies indicate that the His⁶ residue may be a critical factor in determining receptor selectivity for MC1-R (peripheral) versus MC4-R (brain). Three-dimensional molecular models of the human melanocortin receptor have been developed based upon the electron cryo-microscopic structure of bacteriorhodopsin and the electron density footprint of bovine rhodopsin. By modeling known potent agonists into the proposed binding sites, specific ligand-receptor interactions have been identified. By this means, researchers have tentatively identified melanotropin side-chain pharmacophores, D-Phe⁷ and Trp⁹, and have proposed that these interact with a hydrophobic network of receptor aromatic residues in transmembrane regions 4, 5, 6, and 7. The findings of these results are utilized in selecting N-terminal modifications for the metallopeptide core. Groups with hydrophobic and/or hydrogen bonding potential are investigated in a systematic and stereospecific manner, with contemporaneous assaying of potency and MC1-R specificity of the resulting metallopeptides. The influence of the His residue on bioactivity is also investigated. Two series of metallopeptides are synthesized:

-   -   Rheniumoxo-[R-His-D-Phe-Arg-Cys-Trp-NH₂] and     -   Rheniumoxo-[R-D-Phe-Arg-Cys-Trp-NH₂]         where R is a pair consisting of a hydrophobic side chain and         hydrophilc side chain with hydrogen bonding potential which is         selected from the following groups:         and where n is from 2 to 9 and X and/or Y are selected from H,         OH, Cl, Br, I, NH₂, OCH₃, NO₂ and similar groups.

EXAMPLE 8 Skin Darkening in Anolis Carolinensis

PT-1145 complexed with rhenium (0.65 mg taken in a 50 mL vehicle) was injected intraperitoneally in a lizard (Anolis carolinensis) that was pre-conditioned for a skin darkening experiment. The pre-conditioning involved leaving the lizards in a well-lit white background for 24 hours. Within 10-15 minutes after injection, the skin coat color turned from bright green to dark brown to black. The skin coat color remained dark during the five-hour observation period. Lizards injected with the vehicle alone (PBS buffer containing 1% each of DMF and beta-cyclodextran) did not show any change in their skin color during the 5-hour observation period.

Each of the foregoing is merely illustrative, and other equivalent embodiments are possible and contemplated.

Although this invention has been described with reference to these preferred embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents. The entire disclosures of all applications, patents, and publications cited above are hereby incorporated by reference.

The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples. 

1. A combinatorial library targeted to melanocortin receptors of different sequence peptide members synthesized on solid phase, where each constituent library member comprises: (a) a peptide sequence of three or more amino acid residues bound to solid phase characterized by (i) a sequence of two or more amino acid residues forming a metal ion-binding domain and including at least one amino acid residue containing at least one sulfur atom (S) wherein the said S is protected by an orthogonal S-protecting group, (ii) a sequence of one or more amino acid residues at the N- or C-terminus of the metal ion-binding domain, or at both the N- and C-terminus of the metal ion-binding domain, and (iii) a cleavable bond attaching the peptide sequence to solid phase; and (b) a unique selection or sequence of amino acid residues in the peptide sequence of at least one of the constituent members of the library; wherein the orthogonal S-protecting group may be removed without cleaving the peptide sequence from the solid phase.
 2. The combinatorial library of claim 1 wherein the peptide sequence of three or more amino acid residues bound to solid phase is of the formulas: R₁-Lll-Aaa-Bbb-Ccc-R₂, R₁-Bbb-Aaa-Ccc-R₂, R₁-Ddd-Bbb-Aaa-R₃, R₄-Eee-Bbb-Ccc-R₂, R₁-Hhh-Aaa-Bbb-Ccc-R₅, or R₁-Iii-Iii-Ccc-Jjj-Kkk-R₂, wherein R₁ comprises a functionality that potentiates the intrinsic activity of the remainder of the peptide, including but not limited to providing an auxiliary or secondary receptor contact; Aaa is an L- or D-configuration cationic amino acid with a positively charged side chain; Bbb is an L- or D-configuration amino acid with an aromatic side chain; Ccc is an amino acid that provides both a nitrogen atom (N), from the alpha amino group, and a S, from a side chain group, for metal ion complexation; Lll is a D-configuration amino acid with an aromatic side chain; R₂ is optionally present, and if present, comprises an amino acid with an aromatic side chain; Ddd is an amino acid that provides an S, from a side chain group, for metal ion complexation; R₃ is an amino acid with an aromatic side chain that provides an N for metal ion complexation; R₄ is a functionality that provides a cationic center; Eee is an uncharged L- or D-configuration amino acid that provides an N for metal ion complexation; R₅ is an amide, substituted amide, ester or carboxylate group, or comprises an L- or D-configuration amino acid; Hhh is an L- or D-configuration cationic amino acid with a positively charged side chain; Iii is an L- or D-configuration amino acid that provides an N for metal ion complexation; Jjj is an L- or D-configuration amino acid with an aromatic side chain; and Kkk is an L- or D-configuration cationic amino acid with a positively charged side chain.
 3. The combinatorial library of claim 1 wherein the peptide sequence of three or more amino acid residues bound to solid phase is of the formula: R₁-Fff-Aaa-Ggg-Ccc-R₅, wherein R₁ comprises a functionality that potentiates the intrinsic activity of the remainder of the peptide, including but not limited to providing an auxiliary or secondary receptor contact; Aaa is an L- or D-configuration cationic amino acid with a positively charged side chain; Ccc is an amino acid that provides both a N, from the alpha amino group, and a S, from a side chain group, for metal ion complexation; Fff is an L- or D-configuration aromatic amino acid wherein the aromatic ring of the aromatic side chain of Fff is substituted with halogen, alkyl or aryl groups, an L-configuration Phe, or an L- or D-configuration Hphe, Pgl, Trp, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl), Cys(Bzl), Tyr(BzlCl₂), Tic, Tiq or Tca, or derivative, analog or homolog thereof; Ggg is an L- or D-configuration aromatic amino acid; and R₅ is an amide, substituted amide, ester or carboxylate group, or comprises an L- or D-configuration amino acid.
 4. The combinatorial library of claim 1 wherein the peptide sequence of three or more amino acid residues bound to solid phase is of the formula: R₁-Fff-Aaa-Ggg-Ccc-R₅, wherein R₁ comprises a functionality that potentiates the intrinsic activity of the remainder of the peptide, including but not limited to providing an auxiliary or secondary receptor contact; Aaa is an L- or D-configuration cationic amino acid with a positively charged side chain; Ccc is an amino acid that provides both a N, from the alpha amino group, and a S, from a side chain group, for metal ion complexation; Fff is an L- or D-configuration aromatic amino acid; Ggg is an L- or D-configuration aromatic amino acid wherein the aromatic ring of the aromatic side chain of Ggg is substituted with halogen, alkyl or aryl groups, an L-configuration Phe, or an L- or D-configuration Hphe, Pgl, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl), Cys(Bzl) or Tyr(BzlCl₂), and derivatives, analogs or homologs thereof, including both natural and synthetic amino acids; and R₅ is an amide, substituted amide, ester or carboxylate group, or comprises an L- or D-configuration amino acid.
 5. The combinatorial library of claim 1 wherein the metal ion-binding domain further comprises at least one N available for binding to a metal ion upon removal of the orthogonal S-protecting group.
 6. The combinatorial library of claim 1 wherein the orthogonal S-protecting group is S-thio-butyl, acetamidomethyl, 4-methoxytrityl, S-sulfonate or 3-nitro-2-pyridinesulfenyl.
 7. The combinatorial library of claim 1 wherein one or more constituent library members include at least one amino acid residue in the sequence at the N- or C-terminus of the metal ion-binding domain containing at least one S wherein the said S is protected by a non-orthogonal S-protecting group, whereby the orthogonal S-protecting group may be removed without removing the non-orthogonal S-protecting group.
 8. The combinatorial library of claim 1 wherein the at least one amino acid residue containing at least one S wherein the said S is protected by an orthogonal S-protecting group is an L- or D-3-mercapto amino acid, including but not limited to L- or D-cysteine or L- or D-penicillamine; 3-mercapto phenylananine; 2-mercaptoacetic acid; 3-mercaptopropionic acid; 2-mercaptopropionic acid; 3-mercapto-3,3,-dimethyl propionic acid; 3-mercapto-3,3,-diethyl proprionic acid; 3-mercapto,3-methyl propionic acid; 2-mercapto,2-methyl acetic acid; 3-cyclopentamethlene,3-mercaptopropionic acid; or 2-cyclopentamethlene,2-mercaptoacetic acid.
 9. A combinatorial library targeted to melanocortin receptors of different sequence peptide members synthesized on solid phase and complexed to a metal ion, where each constituent library member comprises: (a) a peptide sequence of three or more amino acid residues bound to solid phase characterized by (i) a sequence of two or more amino acid residues forming a metal ion-binding domain and including at least one amino acid residue containing at least one S not protected by a S-protecting group, (ii) a sequence of one or more amino acid residues at the N- or C-terminus of the metal ion-binding domain, or at both the N- and C-terminus of the metal ion-binding domain, and (iii) a cleavable bond attaching the peptide sequence to solid phase; (b) a metal ion complexed to the metal ion-binding domain; and (c) a unique selection or sequence of amino acid residues in the peptide sequence of at least one of the constituent members of the library.
 10. The combinatorial library of claim 9 wherein the peptide sequence of three or more amino acid residues bound to solid phase is of the formulas: R₁-Lll-Aaa-Bbb-Ccc-R₂, R₁-Bbb-Aaa-Ccc-R₂, R₁-Ddd-Bbb-Aaa-R₃, R₄-Eee-Bbb-Ccc-R₂, R₁-Hhh-Aaa-Bbb-Ccc-R₅, or R₁-Iii-Iii-Ccc-Jjj-Kkk-R₂, wherein R₁ comprises a functionality that potentiates the intrinsic activity of the remainder of the peptide, including but not limited to providing an auxiliary or secondary receptor contact; Aaa is an L- or D-configuration cationic amino acid with a positively charged side chain; Bbb is an L- or D-configuration amino acid with an aromatic side chain; Ccc is an amino acid that provides both a N, from the alpha amino group, and a S, from a side chain group, for metal ion complexation; Lll is a D-configuration amino acid with an aromatic side chain; R₂ is optionally present, and if present, comprises an amino acid with an aromatic side chain; Ddd is an amino acid that provides an S, from a side chain group, for metal ion complexation; R₃ is an amino acid with an aromatic side chain that provides an N for metal ion complexation; R₄ is a functionality that provides a cationic center; Eee is an uncharged L- or D-configuration amino acid that provides an N for metal ion complexation; R₅ is an amide, substituted amide, ester or carboxylate group, or comprises an L- or D-configuration amino acid; Hhh is an L- or D-configuration cationic amino acid with a positively charged side chain; Iii is an L- or D-configuration amino acid that provides an N for metal ion complexation; Jjj is an L- or D-configuration amino acid with an aromatic side chain; and Kkk is an L- or D-configuration cationic amino acid with a positively charged side chain.
 11. The combinatorial library of claim 9 wherein the peptide sequence of three or more amino acid residues bound to solid phase is of the formula: R₁-Fff-Aaa-Ggg-Ccc-R₅, wherein R₁ comprises a functionality that potentiates the intrinsic activity of the remainder of the peptide, including but not limited to providing an auxiliary or secondary receptor contact; Aaa is an L- or D-configuration cationic amino acid with a positively charged side chain; Ccc is an amino acid that provides both a N, from the alpha amino group, and a S, from a side chain group, for metal ion complexation; Fff is an L- or D-configuration aromatic amino acid wherein the aromatic ring of the aromatic side chain of Fff is substituted with halogen, alkyl or aryl groups, an L-configuration Phe or an L- or D-configuration Hphe, Pgl, Trp, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl), Cys(Bzl), Tyr(BzlCl₂), Tic, Tiq or Tca, or derivative, analog or homolog thereof; Ggg is an L- or D-configuration aromatic amino acid; and R₅ is an amide, substituted amide, ester or carboxylate group, or comprises an L- or D-configuration amino acid.
 12. The combinatorial library of claim 9 wherein the peptide sequence of three or more amino acid residues bound to solid phase is of the formula: R₁-Fff-Aaa-Ggg-Ccc-R₅, wherein R₁ comprises a functionality that potentiates the intrinsic activity of the remainder of the peptide, including but not limited to providing an auxiliary or secondary receptor contact; Aaa is an L- or D-configuration cationic amino acid with a positively charged side chain; Ccc is an amino acid that provides both a N, from the alpha amino group, and a S, from a side chain group, for metal ion complexation; Fff is an L- or D-configuration aromatic amino acid; Ggg is an L- or D-configuration aromatic amino acid wherein the aromatic ring of the aromatic side chain of Ggg is substituted with halogen, alkyl or aryl groups, or an L-configuration Phe, or an L- or D-configuration Hphe, Pgl, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl), Cys(Bzl) or Tyr(BzlCl₂), and derivatives, analogs or homologs thereof, including both natural and synthetic amino acids; and R₅ is an amide, substituted amide, ester or carboxylate group, or comprises an L- or D-configuration amino acid.
 13. The combinatorial library of claim 9 wherein one or more constituent library members include at least one amino acid residue in the sequence at the N- or C-terminus of the metal ion-binding domain containing at least one S wherein the said S is protected by a S-protecting group.
 14. The combinatorial library of claim 9 wherein the at least one amino acid residue containing at least one S wherein the said S is protected by an orthogonal S-protecting group is an L- or D-3-mercapto amino acid, including but not limited to L- or D-cysteine or L- or D-penicillamine; 3-mercapto phenylananine; 2-mercaptoacetic acid; 3-mercaptopropionic acid; 2-mercaptopropionic acid; 3-mercapto-3,3,-dimethyl propionic acid; 3-mercapto-3,3,-diethyl proprionic acid; 3-mercapto, 3-methyl propionic acid; 2-mercapto,2-methyl acetic acid; 3-cyclopentamethlene,3-mercaptopropionic acid; or 2-cyclopentamethlene,2-mercaptoacetic acid.
 15. The combinatorial library of claim 9 wherein the metal ion is an ionic form of rhenium or technetium.
 16. A combinatorial library targeted to melanocortin receptors of different sequence peptide members synthesized in solution, where each constituent library member comprises: (a) a peptide sequence of a combination of three or more amino acid residues characterized by (i) a sequence of two or more amino acid residues, mimics of amino acid residues or combinations thereof forming a metal ion-binding domain and including at least one amino acid residue or mimic of an amino acid residue containing at least one S wherein the said S is protected by an orthogonal S-protecting group, (ii) a sequence of one or more amino acid residues, mimics of amino acid residues or combinations thereof at the N- or C-terminus of the metal ion-binding domain, or at both the N- and C-terminus of the metal ion-binding domain; and (b) a unique selection or sequence of amino acid residues, mimics of amino acid residues or combinations thereof in the peptidomimetic sequence of at least one of the constituent members of the library.
 17. The combinatorial library of claim 16 wherein the peptide sequence of three or more amino acid residues is of the formulas: R₁-Lll-Aaa-Bbb-Ccc-R₂, R₁-Bbb-Aaa-Ccc-R₂, R₁-Ddd-Bbb-Aaa-R₃, R₄-Eee-Bbb-Ccc-R₂, R₁-Hhh-Aaa-Bbb-Ccc-R₅, or R₁-Iii-Iii-Ccc-Jjj-Kkk-R₂, wherein R₁ comprises a functionality that potentiates the intrinsic activity of the remainder of the peptide, including but not limited to providing an auxiliary or secondary receptor contact; Aaa is an L- or D-configuration cationic amino acid with a positively charged side chain; Bbb is an L- or D-configuration amino acid with an aromatic side chain; Ccc is an amino acid that provides both a N, from the alpha amino group, and a S, from a side chain group, for metal ion complexation; Lll is a D-configuration amino acid with an aromatic side chain; R₂ is optionally present, and if present, comprises an amino acid with an aromatic side chain; Ddd is an amino acid that provides an S, from a side chain group, for metal ion complexation; R₃ is an amino acid with an aromatic side chain that provides an N for metal ion complexation; R₄ is a functionality that provides a cationic center; Eee is an uncharged L- or D-configuration amino acid that provides an N for metal ion complexation; R₅ is an amide, substituted amide, ester or carboxylate group, or comprises an L- or D-configuration amino acid; Hhh is an L- or D-configuration cationic amino acid with a positively charged side chain; Iii is an L- or D-configuration amino acid that provides an N for metal ion complexation; Jjj is an L- or D-configuration amino acid with an aromatic side chain; and Kkk is an L- or D-configuration cationic amino acid with a positively charged side chain.
 18. The combinatorial library of claim 16 wherein the peptide sequence of three or more amino acid residues is of the formula: R₁-Fff-Aaa-Ggg-Ccc-R₅, wherein R₁ comprises a functionality that potentiates the intrinsic activity of the remainder of the peptide, including but not limited to providing an auxiliary or secondary receptor contact; Aaa is an L- or D-configuration cationic amino acid with a positively charged side chain; Ccc is an amino acid that provides both a N, from the alpha amino group, and a S, from a side chain group, for metal ion complexation; Fff is an L- or D-configuration aromatic amino acid wherein the aromatic ring of the aromatic side chain of Fff is substituted with halogen, alkyl or aryl groups, an L-configuration Phe or an L- or D-configuration Hphe, Pgl, Trp, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl), Cys(Bzl), Tyr(BzlCl₂), Tic, Tiq or Tca, or derivative, analog or homolog thereof; Ggg is an L- or D-configuration aromatic amino acid; and R₅ is an amide, substituted amide, ester or carboxylate group, or comprises an L- or D-configuration amino acid.
 19. The combinatorial library of claim 16 wherein the peptide sequence of three or more amino acid residues is of the formula: R₁-Fff-Aaa-Ggg-Ccc-R₅, wherein R₁ comprises a functionality that potentiates the intrinsic activity of the remainder of the peptide, including but not limited to providing an auxiliary or secondary receptor contact; Aaa is an L- or D-configuration cationic amino acid with a positively charged side chain; Ccc is an amino acid that provides both a N, from the alpha amino group, and a S, from a side chain group, for metal ion complexation; Fff is an L- or D-configuration aromatic amino acid; Ggg is an L- or D-configuration aromatic amino acid wherein the aromatic ring of the aromatic side chain of Ggg is substituted with halogen, alkyl or aryl groups, an L-configuration Phe, or an L- or D-configuration Hphe, Pgl, 1-Nal, 2-Nal, Ser(Bzl), Lys(Z), Lys(Z-2′Br), Lys(Bz), Thr(Bzl), Cys(Bzl) or Tyr(BzlCl₂), and derivatives, analogs or homologs thereof, including both natural and synthetic amino acids; and R₅ is an amide, substituted amide, ester or carboxylate group, or comprises an L- or D-configuration amino acid.
 20. The combinatorial library of claim 16 wherein the orthogonal S-protecting group is S-thio-butyl, acetamidomethyl, 4-methoxytrityl, S-sulfonate or 3-nitro-2-pyridinesulfenyl. 